增加一个不可以为Null的字段

• Step 1: Add the Column as Nullable (First PR & Deployment)
  Modify the database schema to add the new column as nullable.
  Update the application code to handle null values and assign a default before inserting data.

SQL Migration

ALTER TABLE MyTable ADD NewColumn INT NULL;

C# Code (Handling Nulls)

public class MyEntity
{
    public int? NewColumn { get; set; } // Nullable field
}

// Ensure default value before inserting

int? newColumnValue = GetValueFromSource();
int finalValue = newColumnValue ?? 0; // Default to 0 if null

Deployment Considerations
✅ Deploy schema changes first
✅ Ensure application logic prevents NULL values from being inserted
✅ Monitor logs for unexpected behavior

• Step 2: Populate Existing Data (Second PR & Deployment)
  Update existing records to ensure all rows have valid values before enforcing NOT NULL.
  SQL Migration

UPDATE MyTable SET NewColumn = 0 WHERE NewColumn IS NULL;

Deployment Considerations
✅ Run data migration scripts in a controlled environment
✅ Validate that all rows have non-null values
✅ Monitor database performance

• Step 3: Enforce NOT NULL Constraint (Third PR & Deployment)
  Once all records have valid values, alter the column to NOT NULL.

SQL Migration

ALTER TABLE MyTable ALTER COLUMN NewColumn INT NOT NULL;

Deployment Considerations
✅ Ensure all inserts provide a valid value
✅ Test thoroughly in staging before deploying
✅ Monitor for unexpected errors

• Step 4: Remove Null Handling Code (Fourth PR & Deployment)
  Since the database now guarantees that the column will always have a value, remove unnecessary null checks.

C# Code (Before Removal)

int? newColumnValue = GetValueFromSource();
int finalValue = newColumnValue ?? 0; // Default to 0 if null

C# Code (After Removal)

int finalValue = GetValueFromSource(); // No need for null handling

Deployment Considerations
✅ Ensure all inserts provide a valid value
✅ Remove unnecessary default assignments
✅ Validate application behavior after deployment

• Best Practices
  🔹 Use Feature Flags – Control rollout via feature flags if applicable
  🔹 Monitor Logs & Errors – Track database changes and application behavior
  🔹 Perform Incremental Rollouts – Deploy changes in small batches
  🔹 Test in Staging First – Validate changes before production deployment