简介
GORM 源码解读, 基于 v1.9.11 版本.
定义模型
GORM 是 ORM, 所以模型定义是最重要的部分, 这一次来探究下具体实现.
type User struct {
gorm.Model
Name string
Age sql.NullInt64
Birthday *time.Time
Email string `gorm:"type:varchar(100);unique_index"`
Role string `gorm:"size:255"` // 设置字段大小为255
MemberNumber *string `gorm:"unique;not null"` // 设置会员号（member number）唯一并且不为空
Num int `gorm:"AUTO_INCREMENT"` // 设置 num 为自增类型
Address string `gorm:"index:addr"` // 给address字段创建名为addr的索引
IgnoreMe int `gorm:"-"` // 忽略本字段
}
这是官方文档上的一个模型定义. 和普通的结构体类似, 但多了属于 gorm 的 tags.
所有的模型都应该包含 gorm.Model, 看一下它的定义:
// Model base model definition, including fields `ID`, `CreatedAt`, `UpdatedAt`, `DeletedAt`, which could be embedded in your models
// type User struct {
// gorm.Model
// }
type Model struct {
ID uint `gorm:"primary_key"`
CreatedAt time.Time
UpdatedAt time.Time
DeletedAt *time.Time `sql:"index"`
}
当然, 这并不是强制要求, 也可以不包含 gorm.Model, 它只是定义了一些非常基础且实用的字段.
定义表的时候, 文档上介绍了很多预设, 比如默认 ID 是表的主键, 表名是结构体名称的复数等.
ModelStruct
要深入了解模型定义, 要从 ModelStruct 开始:
// ModelStruct model definition
type ModelStruct struct {
PrimaryFields []*StructField
StructFields []*StructField
ModelType reflect.Type
defaultTableName string
l sync.Mutex
}
ModelStruct 定义了模型结构体的轮廓, 包含主键字段的切片, 普通字段的切片, 模型类型, 默认表名.
获取表名
ModelStruct 有一个方法获取模型的表名, 看一下它的具体代码:
// TableName returns model's table name
func (s *ModelStruct) TableName(db *DB) string {
s.l.Lock()
defer s.l.Unlock()
if s.defaultTableName == "" && db != nil && s.ModelType != nil {
// Set default table name
if tabler, ok := reflect.New(s.ModelType).Interface().(tabler); ok {
s.defaultTableName = tabler.TableName()
} else {
tableName := ToTableName(s.ModelType.Name())
db.parent.RLock()
if db == nil || (db.parent != nil && !db.parent.singularTable) {
tableName = inflection.Plural(tableName)
}
db.parent.RUnlock()
s.defaultTableName = tableName
}
}
return DefaultTableNameHandler(db, s.defaultTableName)
}
首先, 使用反射检查是否实现了 tabler 接口, 如果实现了, 直接调用 TableName() 方法;
没有实现就使用 ToTableName 转换表名, 有条件地将表名转换为复数形式;
最后一步, 对于所有的表名使用 DefaultTableNameHandler 钩子函数进行再次转换.
看过源码之后, 就能更好的理解文档上关于表名的说明了.
StructField
看一下 StructField 的定义, 即表中的字段是如何表示的:
// StructField model field's struct definition
type StructField struct {
DBName string
Name string
Names []string
IsPrimaryKey bool
IsNormal bool
IsIgnored bool
IsScanner bool
HasDefaultValue bool
Tag reflect.StructTag
TagSettings map[string]string
Struct reflect.StructField
IsForeignKey bool
Relationship *Relationship
tagSettingsLock sync.RWMutex
}
定义了很多字段, 从字段的名字中可以猜测出很多信息, 比如该字段是否是主键等.
注意到有个 TagSettings 字段, 以及配套的 tagSettingsLock 读写锁.
// TagSettingsSet Sets a tag in the tag settings map
func (sf *StructField) TagSettingsSet(key, val string) {
sf.tagSettingsLock.Lock()
defer sf.tagSettingsLock.Unlock()
sf.TagSettings[key] = val
}
// TagSettingsGet returns a tag from the tag settings
func (sf *StructField) TagSettingsGet(key string) (string, bool) {
sf.tagSettingsLock.RLock()
defer sf.tagSettingsLock.RUnlock()
val, ok := sf.TagSettings[key]
return val, ok
}
// TagSettingsDelete deletes a tag
func (sf *StructField) TagSettingsDelete(key string) {
sf.tagSettingsLock.Lock()
defer sf.tagSettingsLock.Unlock()
delete(sf.TagSettings, key)
}
这些方法都是和 TagSettings 有关的, 也可以看作是读写锁 sync.RWMutex 的使用范例.
最后一个方法是关于复制结构体的.
func (sf *StructField) clone() *StructField {
clone := &StructField{
DBName: sf.DBName,
Name: sf.Name,
Names: sf.Names,
IsPrimaryKey: sf.IsPrimaryKey,
IsNormal: sf.IsNormal,
IsIgnored: sf.IsIgnored,
IsScanner: sf.IsScanner,
HasDefaultValue: sf.HasDefaultValue,
Tag: sf.Tag,
TagSettings: map[string]string{},
Struct: sf.Struct,
IsForeignKey: sf.IsForeignKey,
}
if sf.Relationship != nil {
relationship := *sf.Relationship
clone.Relationship = &relationship
}
// copy the struct field tagSettings, they should be read-locked while they are copied
sf.tagSettingsLock.Lock()
defer sf.tagSettingsLock.Unlock()
for key, value := range sf.TagSettings {
clone.TagSettings[key] = value
}
return clone
}
复制 tagSettingsLock 中的字段时, 也用到了读锁.
Relationship
结构体 Relationship 定义了关系类型.
type Relationship struct {
Kind string
PolymorphicType string
PolymorphicDBName string
PolymorphicValue string
ForeignFieldNames []string
ForeignDBNames []string
AssociationForeignFieldNames []string
AssociationForeignDBNames []string
JoinTableHandler JoinTableHandlerInterface
}
func getForeignField(column string, fields []*StructField) *StructField {
for _, field := range fields {
if field.Name == column || field.DBName == column || field.DBName == ToColumnName(column) {
return field
}
}
return nil
}
更多
在继续探索如何解析模型定义之前, 先来了解一下 Scope 结构体.
Scope
// Scope contain current operation's information when you perform any operation on the database
type Scope struct {
Search *search
Value interface{}
SQL string
SQLVars []interface{}
db *DB
instanceID string
primaryKeyField *Field
skipLeft bool
fields *[]*Field
selectAttrs *[]string
}
Scope 是非常重要的一部分, 注释中写道, 当你在数据库上执行任何操作时, Scope 都会记录当前操作的信息.
// IndirectValue return scope's reflect value's indirect value
func (scope *Scope) IndirectValue() reflect.Value {
return indirect(reflect.ValueOf(scope.Value))
}
func indirect(reflectValue reflect.Value) reflect.Value {
for reflectValue.Kind() == reflect.Ptr {
reflectValue = reflectValue.Elem()
}
return reflectValue
}
// New create a new Scope without search information
func (scope *Scope) New(value interface{}) *Scope {
return &Scope{db: scope.NewDB(), Search: &search{}, Value: value}
}
// NewDB create a new DB without search information
func (scope *Scope) NewDB() *DB {
if scope.db != nil {
db := scope.db.clone()
db.search = nil
db.Value = nil
return db
}
return nil
}
Scope 下有很多方法, 先暂时不看. 对它的结构有所了解之后, 回到模型解析上来.
模型解析
用户定义模型之后, 就需要解析模型, 而这个工作是在 Scope 范围内完成的, 所以是其上的方法.
代码很长, 先略览它个大概, 感受一下整体结构.
// GetModelStruct get value's model struct, relationships based on struct and tag definition
func (scope *Scope) GetModelStruct() *ModelStruct {
var modelStruct ModelStruct
// Scope value can't be nil
if scope.Value == nil {
return &modelStruct
}
reflectType := reflect.ValueOf(scope.Value).Type()
for reflectType.Kind() == reflect.Slice || reflectType.Kind() == reflect.Ptr {
reflectType = reflectType.Elem()
}
// Scope value need to be a struct
if reflectType.Kind() != reflect.Struct {
return &modelStruct
}
// Get Cached model struct
isSingularTable := false
if scope.db != nil && scope.db.parent != nil {
scope.db.parent.RLock()
isSingularTable = scope.db.parent.singularTable
scope.db.parent.RUnlock()
}
hashKey := struct {
singularTable bool
reflectType reflect.Type
}{isSingularTable, reflectType}
if value, ok := modelStructsMap.Load(hashKey); ok && value != nil {
return value.(*ModelStruct)
}
modelStruct.ModelType = reflectType
// Get all fields
for i := 0; i < reflectType.NumField(); i++ {
if fieldStruct := reflectType.Field(i); ast.IsExported(fieldStruct.Name) {
field := &StructField{
Struct: fieldStruct,
Name: fieldStruct.Name,
Names: []string{fieldStruct.Name},
Tag: fieldStruct.Tag,
TagSettings: parseTagSetting(fieldStruct.Tag),
}
// is ignored field
if _, ok := field.TagSettingsGet("-"); ok {
field.IsIgnored = true
} else {
if _, ok := field.TagSettingsGet("PRIMARY_KEY"); ok {
field.IsPrimaryKey = true
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, field)
}
if _, ok := field.TagSettingsGet("DEFAULT"); ok && !field.IsPrimaryKey {
field.HasDefaultValue = true
}
if _, ok := field.TagSettingsGet("AUTO_INCREMENT"); ok && !field.IsPrimaryKey {
field.HasDefaultValue = true
}
indirectType := fieldStruct.Type
for indirectType.Kind() == reflect.Ptr {
indirectType = indirectType.Elem()
}
fieldValue := reflect.New(indirectType).Interface()
if _, isScanner := fieldValue.(sql.Scanner); isScanner {
// is scanner
field.IsScanner, field.IsNormal = true, true
if indirectType.Kind() == reflect.Struct {
for i := 0; i < indirectType.NumField(); i++ {
for key, value := range parseTagSetting(indirectType.Field(i).Tag) {
if _, ok := field.TagSettingsGet(key); !ok {
field.TagSettingsSet(key, value)
}
}
}
}
} else if _, isTime := fieldValue.(*time.Time); isTime {
// is time
field.IsNormal = true
} else if _, ok := field.TagSettingsGet("EMBEDDED"); ok || fieldStruct.Anonymous {
// is embedded struct
for _, subField := range scope.New(fieldValue).GetModelStruct().StructFields {
subField = subField.clone()
subField.Names = append([]string{fieldStruct.Name}, subField.Names...)
if prefix, ok := field.TagSettingsGet("EMBEDDED_PREFIX"); ok {
subField.DBName = prefix + subField.DBName
}
if subField.IsPrimaryKey {
if _, ok := subField.TagSettingsGet("PRIMARY_KEY"); ok {
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, subField)
} else {
subField.IsPrimaryKey = false
}
}
if subField.Relationship != nil && subField.Relationship.JoinTableHandler != nil {
if joinTableHandler, ok := subField.Relationship.JoinTableHandler.(*JoinTableHandler); ok {
newJoinTableHandler := &JoinTableHandler{}
newJoinTableHandler.Setup(subField.Relationship, joinTableHandler.TableName, reflectType, joinTableHandler.Destination.ModelType)
subField.Relationship.JoinTableHandler = newJoinTableHandler
}
}
modelStruct.StructFields = append(modelStruct.StructFields, subField)
}
continue
} else {
// build relationships
switch indirectType.Kind() {
case reflect.Slice:
defer func(field *StructField) {
var (
relationship = &Relationship{}
toScope = scope.New(reflect.New(field.Struct.Type).Interface())
foreignKeys []string
associationForeignKeys []string
elemType = field.Struct.Type
)
if foreignKey, _ := field.TagSettingsGet("FOREIGNKEY"); foreignKey != "" {
foreignKeys = strings.Split(foreignKey, ",")
}
if foreignKey, _ := field.TagSettingsGet("ASSOCIATION_FOREIGNKEY"); foreignKey != "" {
associationForeignKeys = strings.Split(foreignKey, ",")
} else if foreignKey, _ := field.TagSettingsGet("ASSOCIATIONFOREIGNKEY"); foreignKey != "" {
associationForeignKeys = strings.Split(foreignKey, ",")
}
for elemType.Kind() == reflect.Slice || elemType.Kind() == reflect.Ptr {
elemType = elemType.Elem()
}
if elemType.Kind() == reflect.Struct {
if many2many, _ := field.TagSettingsGet("MANY2MANY"); many2many != "" {
relationship.Kind = "many_to_many"
{ // Foreign Keys for Source
joinTableDBNames := []string{}
if foreignKey, _ := field.TagSettingsGet("JOINTABLE_FOREIGNKEY"); foreignKey != "" {
joinTableDBNames = strings.Split(foreignKey, ",")
}
// if no foreign keys defined with tag
if len(foreignKeys) == 0 {
for _, field := range modelStruct.PrimaryFields {
foreignKeys = append(foreignKeys, field.DBName)
}
}
for idx, foreignKey := range foreignKeys {
if foreignField := getForeignField(foreignKey, modelStruct.StructFields); foreignField != nil {
// source foreign keys (db names)
relationship.ForeignFieldNames = append(relationship.ForeignFieldNames, foreignField.DBName)
// setup join table foreign keys for source
if len(joinTableDBNames) > idx {
// if defined join table's foreign key
relationship.ForeignDBNames = append(relationship.ForeignDBNames, joinTableDBNames[idx])
} else {
defaultJointableForeignKey := ToColumnName(reflectType.Name()) + "_" + foreignField.DBName
relationship.ForeignDBNames = append(relationship.ForeignDBNames, defaultJointableForeignKey)
}
}
}
}
{ // Foreign Keys for Association (Destination)
associationJoinTableDBNames := []string{}
if foreignKey, _ := field.TagSettingsGet("ASSOCIATION_JOINTABLE_FOREIGNKEY"); foreignKey != "" {
associationJoinTableDBNames = strings.Split(foreignKey, ",")
}
// if no association foreign keys defined with tag
if len(associationForeignKeys) == 0 {
for _, field := range toScope.PrimaryFields() {
associationForeignKeys = append(associationForeignKeys, field.DBName)
}
}
for idx, name := range associationForeignKeys {
if field, ok := toScope.FieldByName(name); ok {
// association foreign keys (db names)
relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, field.DBName)
// setup join table foreign keys for association
if len(associationJoinTableDBNames) > idx {
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, associationJoinTableDBNames[idx])
} else {
// join table foreign keys for association
joinTableDBName := ToColumnName(elemType.Name()) + "_" + field.DBName
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, joinTableDBName)
}
}
}
}
joinTableHandler := JoinTableHandler{}
joinTableHandler.Setup(relationship, many2many, reflectType, elemType)
relationship.JoinTableHandler = &joinTableHandler
field.Relationship = relationship
} else {
// User has many comments, associationType is User, comment use UserID as foreign key
var associationType = reflectType.Name()
var toFields = toScope.GetStructFields()
relationship.Kind = "has_many"
if polymorphic, _ := field.TagSettingsGet("POLYMORPHIC"); polymorphic != "" {
// Dog has many toys, tag polymorphic is Owner, then associationType is Owner
// Toy use OwnerID, OwnerType ('dogs') as foreign key
if polymorphicType := getForeignField(polymorphic+"Type", toFields); polymorphicType != nil {
associationType = polymorphic
relationship.PolymorphicType = polymorphicType.Name
relationship.PolymorphicDBName = polymorphicType.DBName
// if Dog has multiple set of toys set name of the set (instead of default 'dogs')
if value, ok := field.TagSettingsGet("POLYMORPHIC_VALUE"); ok {
relationship.PolymorphicValue = value
} else {
relationship.PolymorphicValue = scope.TableName()
}
polymorphicType.IsForeignKey = true
}
}
// if no foreign keys defined with tag
if len(foreignKeys) == 0 {
// if no association foreign keys defined with tag
if len(associationForeignKeys) == 0 {
for _, field := range modelStruct.PrimaryFields {
foreignKeys = append(foreignKeys, associationType+field.Name)
associationForeignKeys = append(associationForeignKeys, field.Name)
}
} else {
// generate foreign keys from defined association foreign keys
for _, scopeFieldName := range associationForeignKeys {
if foreignField := getForeignField(scopeFieldName, modelStruct.StructFields); foreignField != nil {
foreignKeys = append(foreignKeys, associationType+foreignField.Name)
associationForeignKeys = append(associationForeignKeys, foreignField.Name)
}
}
}
} else {
// generate association foreign keys from foreign keys
if len(associationForeignKeys) == 0 {
for _, foreignKey := range foreignKeys {
if strings.HasPrefix(foreignKey, associationType) {
associationForeignKey := strings.TrimPrefix(foreignKey, associationType)
if foreignField := getForeignField(associationForeignKey, modelStruct.StructFields); foreignField != nil {
associationForeignKeys = append(associationForeignKeys, associationForeignKey)
}
}
}
if len(associationForeignKeys) == 0 && len(foreignKeys) == 1 {
associationForeignKeys = []string{scope.PrimaryKey()}
}
} else if len(foreignKeys) != len(associationForeignKeys) {
scope.Err(errors.New("invalid foreign keys, should have same length"))
return
}
}
for idx, foreignKey := range foreignKeys {
if foreignField := getForeignField(foreignKey, toFields); foreignField != nil {
if associationField := getForeignField(associationForeignKeys[idx], modelStruct.StructFields); associationField != nil {
// source foreign keys
foreignField.IsForeignKey = true
relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, associationField.Name)
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, associationField.DBName)
// association foreign keys
relationship.ForeignFieldNames = append(relationship.ForeignFieldNames, foreignField.Name)
relationship.ForeignDBNames = append(relationship.ForeignDBNames, foreignField.DBName)
}
}
}
if len(relationship.ForeignFieldNames) != 0 {
field.Relationship = relationship
}
}
} else {
field.IsNormal = true
}
}(field)
case reflect.Struct:
defer func(field *StructField) {
var (
// user has one profile, associationType is User, profile use UserID as foreign key
// user belongs to profile, associationType is Profile, user use ProfileID as foreign key
associationType = reflectType.Name()
relationship = &Relationship{}
toScope = scope.New(reflect.New(field.Struct.Type).Interface())
toFields = toScope.GetStructFields()
tagForeignKeys []string
tagAssociationForeignKeys []string
)
if foreignKey, _ := field.TagSettingsGet("FOREIGNKEY"); foreignKey != "" {
tagForeignKeys = strings.Split(foreignKey, ",")
}
if foreignKey, _ := field.TagSettingsGet("ASSOCIATION_FOREIGNKEY"); foreignKey != "" {
tagAssociationForeignKeys = strings.Split(foreignKey, ",")
} else if foreignKey, _ := field.TagSettingsGet("ASSOCIATIONFOREIGNKEY"); foreignKey != "" {
tagAssociationForeignKeys = strings.Split(foreignKey, ",")
}
if polymorphic, _ := field.TagSettingsGet("POLYMORPHIC"); polymorphic != "" {
// Cat has one toy, tag polymorphic is Owner, then associationType is Owner
// Toy use OwnerID, OwnerType ('cats') as foreign key
if polymorphicType := getForeignField(polymorphic+"Type", toFields); polymorphicType != nil {
associationType = polymorphic
relationship.PolymorphicType = polymorphicType.Name
relationship.PolymorphicDBName = polymorphicType.DBName
// if Cat has several different types of toys set name for each (instead of default 'cats')
if value, ok := field.TagSettingsGet("POLYMORPHIC_VALUE"); ok {
relationship.PolymorphicValue = value
} else {
relationship.PolymorphicValue = scope.TableName()
}
polymorphicType.IsForeignKey = true
}
}
// Has One
{
var foreignKeys = tagForeignKeys
var associationForeignKeys = tagAssociationForeignKeys
// if no foreign keys defined with tag
if len(foreignKeys) == 0 {
// if no association foreign keys defined with tag
if len(associationForeignKeys) == 0 {
for _, primaryField := range modelStruct.PrimaryFields {
foreignKeys = append(foreignKeys, associationType+primaryField.Name)
associationForeignKeys = append(associationForeignKeys, primaryField.Name)
}
} else {
// generate foreign keys form association foreign keys
for _, associationForeignKey := range tagAssociationForeignKeys {
if foreignField := getForeignField(associationForeignKey, modelStruct.StructFields); foreignField != nil {
foreignKeys = append(foreignKeys, associationType+foreignField.Name)
associationForeignKeys = append(associationForeignKeys, foreignField.Name)
}
}
}
} else {
// generate association foreign keys from foreign keys
if len(associationForeignKeys) == 0 {
for _, foreignKey := range foreignKeys {
if strings.HasPrefix(foreignKey, associationType) {
associationForeignKey := strings.TrimPrefix(foreignKey, associationType)
if foreignField := getForeignField(associationForeignKey, modelStruct.StructFields); foreignField != nil {
associationForeignKeys = append(associationForeignKeys, associationForeignKey)
}
}
}
if len(associationForeignKeys) == 0 && len(foreignKeys) == 1 {
associationForeignKeys = []string{scope.PrimaryKey()}
}
} else if len(foreignKeys) != len(associationForeignKeys) {
scope.Err(errors.New("invalid foreign keys, should have same length"))
return
}
}
for idx, foreignKey := range foreignKeys {
if foreignField := getForeignField(foreignKey, toFields); foreignField != nil {
if scopeField := getForeignField(associationForeignKeys[idx], modelStruct.StructFields); scopeField != nil {
foreignField.IsForeignKey = true
// source foreign keys
relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, scopeField.Name)
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, scopeField.DBName)
// association foreign keys
relationship.ForeignFieldNames = append(relationship.ForeignFieldNames, foreignField.Name)
relationship.ForeignDBNames = append(relationship.ForeignDBNames, foreignField.DBName)
}
}
}
}
if len(relationship.ForeignFieldNames) != 0 {
relationship.Kind = "has_one"
field.Relationship = relationship
} else {
var foreignKeys = tagForeignKeys
var associationForeignKeys = tagAssociationForeignKeys
if len(foreignKeys) == 0 {
// generate foreign keys & association foreign keys
if len(associationForeignKeys) == 0 {
for _, primaryField := range toScope.PrimaryFields() {
foreignKeys = append(foreignKeys, field.Name+primaryField.Name)
associationForeignKeys = append(associationForeignKeys, primaryField.Name)
}
} else {
// generate foreign keys with association foreign keys
for _, associationForeignKey := range associationForeignKeys {
if foreignField := getForeignField(associationForeignKey, toFields); foreignField != nil {
foreignKeys = append(foreignKeys, field.Name+foreignField.Name)
associationForeignKeys = append(associationForeignKeys, foreignField.Name)
}
}
}
} else {
// generate foreign keys & association foreign keys
if len(associationForeignKeys) == 0 {
for _, foreignKey := range foreignKeys {
if strings.HasPrefix(foreignKey, field.Name) {
associationForeignKey := strings.TrimPrefix(foreignKey, field.Name)
if foreignField := getForeignField(associationForeignKey, toFields); foreignField != nil {
associationForeignKeys = append(associationForeignKeys, associationForeignKey)
}
}
}
if len(associationForeignKeys) == 0 && len(foreignKeys) == 1 {
associationForeignKeys = []string{toScope.PrimaryKey()}
}
} else if len(foreignKeys) != len(associationForeignKeys) {
scope.Err(errors.New("invalid foreign keys, should have same length"))
return
}
}
for idx, foreignKey := range foreignKeys {
if foreignField := getForeignField(foreignKey, modelStruct.StructFields); foreignField != nil {
if associationField := getForeignField(associationForeignKeys[idx], toFields); associationField != nil {
foreignField.IsForeignKey = true
// association foreign keys
relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, associationField.Name)
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, associationField.DBName)
// source foreign keys
relationship.ForeignFieldNames = append(relationship.ForeignFieldNames, foreignField.Name)
relationship.ForeignDBNames = append(relationship.ForeignDBNames, foreignField.DBName)
}
}
}
if len(relationship.ForeignFieldNames) != 0 {
relationship.Kind = "belongs_to"
field.Relationship = relationship
}
}
}(field)
default:
field.IsNormal = true
}
}
}
// Even it is ignored, also possible to decode db value into the field
if value, ok := field.TagSettingsGet("COLUMN"); ok {
field.DBName = value
} else {
field.DBName = ToColumnName(fieldStruct.Name)
}
modelStruct.StructFields = append(modelStruct.StructFields, field)
}
}
if len(modelStruct.PrimaryFields) == 0 {
if field := getForeignField("id", modelStruct.StructFields); field != nil {
field.IsPrimaryKey = true
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, field)
}
}
modelStructsMap.Store(hashKey, &modelStruct)
return &modelStruct
}
其实首先折叠一下中间的 for 循环会好很多.
// GetModelStruct get value's model struct, relationships based on struct and tag definition
func (scope *Scope) GetModelStruct() *ModelStruct {
var modelStruct ModelStruct
// Scope value can't be nil
if scope.Value == nil {
return &modelStruct
}
reflectType := reflect.ValueOf(scope.Value).Type()
for reflectType.Kind() == reflect.Slice || reflectType.Kind() == reflect.Ptr {
reflectType = reflectType.Elem()
}
// Scope value need to be a struct
if reflectType.Kind() != reflect.Struct {
return &modelStruct
}
// Get Cached model struct
isSingularTable := false
if scope.db != nil && scope.db.parent != nil {
scope.db.parent.RLock()
isSingularTable = scope.db.parent.singularTable
scope.db.parent.RUnlock()
}
hashKey := struct {
singularTable bool
reflectType reflect.Type
}{isSingularTable, reflectType}
if value, ok := modelStructsMap.Load(hashKey); ok && value != nil {
return value.(*ModelStruct)
}
modelStruct.ModelType = reflectType
// Get all fields
for i := 0; i < reflectType.NumField(); i++ {
... // 折叠先不看
}
if len(modelStruct.PrimaryFields) == 0 {
if field := getForeignField("id", modelStruct.StructFields); field != nil {
field.IsPrimaryKey = true
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, field)
}
}
modelStructsMap.Store(hashKey, &modelStruct)
return &modelStruct
}
开头初始化了 var modelStruct ModelStruct, 这也是最后要返回的结果.
一开始先判断了 scope.Value 不能为空, 否则就直接返回.
然后解析了 scope.Value 的具体类型, 对于切片或指针, 要看具
reflectType := reflect.ValueOf(scope.Value).Type()
for reflectType.Kind() == reflect.Slice || reflectType.Kind() == reflect.Ptr {
reflectType = reflectType.Elem()
}
如果 scope.Value 的具体类型不是 Struct, 也是直接返回.
然后, 判断是否有 ModelStruct 的缓存:
// Get Cached model struct
isSingularTable := false
if scope.db != nil && scope.db.parent != nil {
scope.db.parent.RLock()
isSingularTable = scope.db.parent.singularTable
scope.db.parent.RUnlock()
}
hashKey := struct {
singularTable bool
reflectType reflect.Type
}{isSingularTable, reflectType}
if value, ok := modelStructsMap.Load(hashKey); ok && value != nil {
return value.(*ModelStruct)
}
modelStructsMap 是定义在外部的, 用于共享缓存.
var modelStructsMap sync.Map
如果可以从 modelStructsMap 找到, 就可以直接返回缓存.
modelStruct.ModelType = reflectType
略过 Get all fields 部分, 直接看后面的部分.
if len(modelStruct.PrimaryFields) == 0 {
if field := getForeignField("id", modelStruct.StructFields); field != nil {
field.IsPrimaryKey = true
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, field)
}
}
如果没有找到主键, 就会把 ID 作为主键.
modelStructsMap.Store(hashKey, &modelStruct)
return &modelStruct
将解析好的结果保存到 modelStructsMap, 作为缓存, 加快后面解析的过程. 最后返回结果.
现在, 已经将整个解析流程看完了, 除了获取字段的过程不清楚, 其他都应该清楚了.
解析的过程中用到了缓存, 也是我们可以借鉴的地方, sync.Map 可以安全地用于 goroutine 中共享.
另一点是将结构体作为 key, 同时兼顾了单数形式的表名和复数形式的表名.
字段解析
前面的过程中省略了解析字段的过程, 这是非常重要的一部分. GetModelStruct 方法的大部分的代码都集中在这一部分中.
for i := 0; i < reflectType.NumField(); i++ {
reflectType.NumField() 可以获取结构体中的字段总数.
if fieldStruct := reflectType.Field(i); ast.IsExported(fieldStruct.Name) {
只解析可以导出的字段. 使用 reflectType.Field(i) 和索引 i, 可以获取到结构体中的字段.
field := &StructField{
Struct: fieldStruct,
Name: fieldStruct.Name,
Names: []string{fieldStruct.Name},
Tag: fieldStruct.Tag,
TagSettings: parseTagSetting(fieldStruct.Tag),
}
StructField 初始化, 可以看到很多信息都是从 fieldStruct 中获取的.
这一部分对于学习如何解析结构体中的 Tag 非常有帮助, 仔细看一下.
fieldStruct.Tag 可以获取字段中的 tag 部分, 比如:
type Model struct {
ID uint `gorm:"primary_key"`
CreatedAt time.Time
UpdatedAt time.Time
DeletedAt *time.Time
}
ID 字段中的 gorm:"primary_key" 部分.
fieldStruct.Name 可以获取字段的名字.
看一下具体是如何解析 Tag 字符串的.
func parseTagSetting(tags reflect.StructTag) map[string]string {
setting := map[string]string{}
for _, str := range []string{tags.Get("sql"), tags.Get("gorm")} {
if str == "" {
continue
}
tags := strings.Split(str, ";")
for _, value := range tags {
v := strings.Split(value, ":")
k := strings.TrimSpace(strings.ToUpper(v[0]))
if len(v) >= 2 {
setting[k] = strings.Join(v[1:], ":")
} else {
setting[k] = k
}
}
}
return setting
}
tags 的类型是 reflect.StructTag, 包含一些实用的方法, 比如 Get 方法可以获取特定的部分.
这里获取了 sql 和 gorm 部分.
每个 tag 部分中, 都是使用 ; 分隔的选项. 每个选项又可能是 key/value 类型的, 由 : 分隔,
也可能是一个单独的值.
具体看一个例子:
type User struct {
gorm.Model
Name string
Age sql.NullInt64
Birthday *time.Time
Email string `gorm:"type:varchar(100);unique_index"`
Role string `gorm:"size:255"` // 设置字段大小为255
MemberNumber *string `gorm:"unique;not null"` // 设置会员号（member number）唯一并且不为空
Num int `gorm:"AUTO_INCREMENT"` // 设置 num 为自增类型
Address string `gorm:"index:addr"` // 给address字段创建名为addr的索引
IgnoreMe int `gorm:"-"` // 忽略本字段
}
比如 Email 字段的 tags 中 gorm 部分有两个选项, 一个是 type:varchar(100), 另一个是 unique_index.
结合上面的 parseTagSetting 代码, 我们知道这个字段的 tags 是如何被解析的了.
对于导出的字段, 也有办法设置忽略该字段, 设置选项为 - 就行了.
// is ignored field
if _, ok := field.TagSettingsGet("-"); ok {
field.IsIgnored = true
}
然后就是解析每一个选项了. 主要的代码都在这里, 一点点看:
if _, ok := field.TagSettingsGet("PRIMARY_KEY"); ok {
field.IsPrimaryKey = true
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, field)
}
if _, ok := field.TagSettingsGet("DEFAULT"); ok && !field.IsPrimaryKey {
field.HasDefaultValue = true
}
if _, ok := field.TagSettingsGet("AUTO_INCREMENT"); ok && !field.IsPrimaryKey {
field.HasDefaultValue = true
}
设置 IsPrimaryKey 和 HasDefaultValue 属性. 如果是主键的话, 还会添加到 PrimaryFields 中.
indirectType := fieldStruct.Type
for indirectType.Kind() == reflect.Ptr {
indirectType = indirectType.Elem()
}
获取字段的类型.
fieldValue := reflect.New(indirectType).Interface()
获取字段对应的值.
然后是根据 fieldValue 的类型进行了一堆判断, 一个个看.
- 判断一
if _, isScanner := fieldValue.(sql.Scanner); isScanner {
// is scanner
field.IsScanner, field.IsNormal = true, true
if indirectType.Kind() == reflect.Struct {
for i := 0; i < indirectType.NumField(); i++ {
for key, value := range parseTagSetting(indirectType.Field(i).Tag) {
if _, ok := field.TagSettingsGet(key); !ok {
field.TagSettingsSet(key, value)
}
}
}
}
}
如果实现了 sql.Scanner 接口, 设置了两个属性为 true.
- 判断二
如果该字段是结构体, 将结构体中的每个 tag 设置都添加一遍.
else if _, isTime := fieldValue.(*time.Time); isTime {
// is time
field.IsNormal = true
}
如果是 *time.Time 结构体, 设置 IsNormal 为 true.
else if _, ok := field.TagSettingsGet("EMBEDDED"); ok || fieldStruct.Anonymous {
// is embedded struct
for _, subField := range scope.New(fieldValue).GetModelStruct().StructFields {
subField = subField.clone()
subField.Names = append([]string{fieldStruct.Name}, subField.Names...)
if prefix, ok := field.TagSettingsGet("EMBEDDED_PREFIX"); ok {
subField.DBName = prefix + subField.DBName
}
if subField.IsPrimaryKey {
if _, ok := subField.TagSettingsGet("PRIMARY_KEY"); ok {
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, subField)
} else {
subField.IsPrimaryKey = false
}
}
if subField.Relationship != nil && subField.Relationship.JoinTableHandler != nil {
if joinTableHandler, ok := subField.Relationship.JoinTableHandler.(*JoinTableHandler); ok {
newJoinTableHandler := &JoinTableHandler{}
newJoinTableHandler.Setup(subField.Relationship, joinTableHandler.TableName, reflectType, joinTableHandler.Destination.ModelType)
subField.Relationship.JoinTableHandler = newJoinTableHandler
}
}
modelStruct.StructFields = append(modelStruct.StructFields, subField)
}
continue
}
- 判断三
如果 tag 设置中有 EMBEDDED 字段, 表示是一个嵌入的结构体.
for _, subField := range scope.New(fieldValue).GetModelStruct().StructFields {
遍历该字段对应的 ModelStruct 中的每个 StructFields 中的 StructField.
subField = subField.clone() 直接在副本上操作.
subField.Names = append([]string{fieldStruct.Name}, subField.Names...)
if prefix, ok := field.TagSettingsGet("EMBEDDED_PREFIX"); ok {
subField.DBName = prefix + subField.DBName
}
重新设置 Names 和 DBName.
if subField.IsPrimaryKey {
if _, ok := subField.TagSettingsGet("PRIMARY_KEY"); ok {
modelStruct.PrimaryFields = append(modelStruct.PrimaryFields, subField)
} else {
subField.IsPrimaryKey = false
}
}
如果 subField 是主键, 且有 PRIMARY_KEY tag 选项, 添加到 modelStruct.PrimaryFields 上去.
否则, 重置 subField.IsPrimaryKey 为 false.
if subField.Relationship != nil && subField.Relationship.JoinTableHandler != nil {
if joinTableHandler, ok := subField.Relationship.JoinTableHandler.(*JoinTableHandler); ok {
newJoinTableHandler := &JoinTableHandler{}
newJoinTableHandler.Setup(subField.Relationship, joinTableHandler.TableName, reflectType, joinTableHandler.Destination.ModelType)
subField.Relationship.JoinTableHandler = newJoinTableHandler
}
}
初始化了 subField 中的 JoinTableHandler.
modelStruct.StructFields = append(modelStruct.StructFields, subField)
最后将 subField 添加到了 modelStruct.StructFields 中.
最后, 使用 continue 开始新的 for 循环. 因此, field.TagSettingsGet("EMBEDDED") 部分也结束了.
- 判断四
如果上面的三个判断都不满足, 就进入了最后的 else 判断了.
而这里面又是个 switch 判断, 真的是忧伤.
根据 switch indirectType.Kind() { 的类型, 主要是切片和结构体, 先看 default 部分:
default:
field.IsNormal = true
}
case reflect.Slice: 和 case reflect.Struct: 里都是一个 defer 函数.
case reflect.Slice:
defer func(field *StructField) {
var (
relationship = &Relationship{}
toScope = scope.New(reflect.New(field.Struct.Type).Interface())
foreignKeys []string
associationForeignKeys []string
elemType = field.Struct.Type
)
if foreignKey, _ := field.TagSettingsGet("FOREIGNKEY"); foreignKey != "" {
foreignKeys = strings.Split(foreignKey, ",")
}
if foreignKey, _ := field.TagSettingsGet("ASSOCIATION_FOREIGNKEY"); foreignKey != "" {
associationForeignKeys = strings.Split(foreignKey, ",")
} else if foreignKey, _ := field.TagSettingsGet("ASSOCIATIONFOREIGNKEY"); foreignKey != "" {
associationForeignKeys = strings.Split(foreignKey, ",")
}
for elemType.Kind() == reflect.Slice || elemType.Kind() == reflect.Ptr {
elemType = elemType.Elem()
}
if elemType.Kind() == reflect.Struct {
if many2many, _ := field.TagSettingsGet("MANY2MANY"); many2many != "" {
relationship.Kind = "many_to_many"
{ // Foreign Keys for Source
joinTableDBNames := []string{}
if foreignKey, _ := field.TagSettingsGet("JOINTABLE_FOREIGNKEY"); foreignKey != "" {
joinTableDBNames = strings.Split(foreignKey, ",")
}
// if no foreign keys defined with tag
if len(foreignKeys) == 0 {
for _, field := range modelStruct.PrimaryFields {
foreignKeys = append(foreignKeys, field.DBName)
}
}
for idx, foreignKey := range foreignKeys {
if foreignField := getForeignField(foreignKey, modelStruct.StructFields); foreignField != nil {
// source foreign keys (db names)
relationship.ForeignFieldNames = append(relationship.ForeignFieldNames, foreignField.DBName)
// setup join table foreign keys for source
if len(joinTableDBNames) > idx {
// if defined join table's foreign key
relationship.ForeignDBNames = append(relationship.ForeignDBNames, joinTableDBNames[idx])
} else {
defaultJointableForeignKey := ToColumnName(reflectType.Name()) + "_" + foreignField.DBName
relationship.ForeignDBNames = append(relationship.ForeignDBNames, defaultJointableForeignKey)
}
}
}
}
{ // Foreign Keys for Association (Destination)
associationJoinTableDBNames := []string{}
if foreignKey, _ := field.TagSettingsGet("ASSOCIATION_JOINTABLE_FOREIGNKEY"); foreignKey != "" {
associationJoinTableDBNames = strings.Split(foreignKey, ",")
}
// if no association foreign keys defined with tag
if len(associationForeignKeys) == 0 {
for _, field := range toScope.PrimaryFields() {
associationForeignKeys = append(associationForeignKeys, field.DBName)
}
}
for idx, name := range associationForeignKeys {
if field, ok := toScope.FieldByName(name); ok {
// association foreign keys (db names)
relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, field.DBName)
// setup join table foreign keys for association
if len(associationJoinTableDBNames) > idx {
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, associationJoinTableDBNames[idx])
} else {
// join table foreign keys for association
joinTableDBName := ToColumnName(elemType.Name()) + "_" + field.DBName
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, joinTableDBName)
}
}
}
}
joinTableHandler := JoinTableHandler{}
joinTableHandler.Setup(relationship, many2many, reflectType, elemType)
relationship.JoinTableHandler = &joinTableHandler
field.Relationship = relationship
} else {
// User has many comments, associationType is User, comment use UserID as foreign key
var associationType = reflectType.Name()
var toFields = toScope.GetStructFields()
relationship.Kind = "has_many"
if polymorphic, _ := field.TagSettingsGet("POLYMORPHIC"); polymorphic != "" {
// Dog has many toys, tag polymorphic is Owner, then associationType is Owner
// Toy use OwnerID, OwnerType ('dogs') as foreign key
if polymorphicType := getForeignField(polymorphic+"Type", toFields); polymorphicType != nil {
associationType = polymorphic
relationship.PolymorphicType = polymorphicType.Name
relationship.PolymorphicDBName = polymorphicType.DBName
// if Dog has multiple set of toys set name of the set (instead of default 'dogs')
if value, ok := field.TagSettingsGet("POLYMORPHIC_VALUE"); ok {
relationship.PolymorphicValue = value
} else {
relationship.PolymorphicValue = scope.TableName()
}
polymorphicType.IsForeignKey = true
}
}
// if no foreign keys defined with tag
if len(foreignKeys) == 0 {
// if no association foreign keys defined with tag
if len(associationForeignKeys) == 0 {
for _, field := range modelStruct.PrimaryFields {
foreignKeys = append(foreignKeys, associationType+field.Name)
associationForeignKeys = append(associationForeignKeys, field.Name)
}
} else {
// generate foreign keys from defined association foreign keys
for _, scopeFieldName := range associationForeignKeys {
if foreignField := getForeignField(scopeFieldName, modelStruct.StructFields); foreignField != nil {
foreignKeys = append(foreignKeys, associationType+foreignField.Name)
associationForeignKeys = append(associationForeignKeys, foreignField.Name)
}
}
}
} else {
// generate association foreign keys from foreign keys
if len(associationForeignKeys) == 0 {
for _, foreignKey := range foreignKeys {
if strings.HasPrefix(foreignKey, associationType) {
associationForeignKey := strings.TrimPrefix(foreignKey, associationType)
if foreignField := getForeignField(associationForeignKey, modelStruct.StructFields); foreignField != nil {
associationForeignKeys = append(associationForeignKeys, associationForeignKey)
}
}
}
if len(associationForeignKeys) == 0 && len(foreignKeys) == 1 {
associationForeignKeys = []string{scope.PrimaryKey()}
}
} else if len(foreignKeys) != len(associationForeignKeys) {
scope.Err(errors.New("invalid foreign keys, should have same length"))
return
}
}
for idx, foreignKey := range foreignKeys {
if foreignField := getForeignField(foreignKey, toFields); foreignField != nil {
if associationField := getForeignField(associationForeignKeys[idx], modelStruct.StructFields); associationField != nil {
// source foreign keys
foreignField.IsForeignKey = true
relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, associationField.Name)
relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, associationField.DBName)
// association foreign keys
relationship.ForeignFieldNames = append(relationship.ForeignFieldNames, foreignField.Name)
relationship.ForeignDBNames = append(relationship.ForeignDBNames, foreignField.DBName)
}
}
}
if len(relationship.ForeignFieldNames) != 0 {
field.Relationship = relationship
}
}
} else {
field.IsNormal = true
}
}(field)
主要是处理了关系类型的 tag.
这一部分先跳过吧, 等具体研究关系的实现, 再继续深入.
等这整个 if 判断都结束后, 解析一下列名, 最后将 fields 添加到 modelStruct.StructFields:
// Even it is ignored, also possible to decode db value into the field
if value, ok := field.TagSettingsGet("COLUMN"); ok {
field.DBName = value
} else {
field.DBName = ToColumnName(fieldStruct.Name)
}
modelStruct.StructFields = append(modelStruct.StructFields, field)
小结
所以, 整个模型解析的过程就是如此. 最耗时的部分在于解析每个字段, 解析 tag 以及字段间的关系.
总结
定义模型并解析模型的过程已经看完了, 但关于模型还有很多内容, 比如将模型转换为表插入数据库等.
