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Optimize default value handling during type changes #210

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Merged
tianzhou merged 2 commits into from
Dec 18, 2025
Merged

Optimize default value handling during type changes #210

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eb7cd1b
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Copilot Dec 18, 2025
00e2eb2
Optimize default value handling for type changes without USING clause
Copilot Dec 18, 2025
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19 changes: 10 additions & 9 deletions internal/diff/column.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,15 +16,16 @@ func (cd *ColumnDiff) generateColumnSQL(tableSchema, tableName string, targetSch
newType := stripSchemaPrefix(cd.New.DataType, targetSchema)

// Check if there's a type change AND the column has a default value
// In this case, we need to: DROP DEFAULT -> ALTER TYPE -> SET DEFAULT
// because PostgreSQL can't automatically cast default values during type changes
// When a USING clause is needed, we must: DROP DEFAULT -> ALTER TYPE -> SET DEFAULT
// because PostgreSQL can't automatically cast default values during type changes with USING
hasTypeChange := oldType != newType
oldDefault := cd.Old.DefaultValue
newDefault := cd.New.DefaultValue
hasOldDefault := oldDefault != nil && *oldDefault != ""
needsUsing := hasTypeChange && needsUsingClause(oldType, newType)

// If type is changing and there's an existing default, drop the default first
if hasTypeChange && hasOldDefault {
// If type is changing with USING clause and there's an existing default, drop the default first
if needsUsing && hasOldDefault {
sql := fmt.Sprintf("ALTER TABLE %s ALTER COLUMN %s DROP DEFAULT;",
qualifiedTableName, cd.New.Name)
statements = append(statements, sql)
Expand All @@ -35,7 +36,7 @@ func (cd *ColumnDiff) generateColumnSQL(tableSchema, tableName string, targetSch
// Check if we need a USING clause for the type conversion
// This is required when converting from text-like types to custom types (like ENUMs)
// because PostgreSQL cannot implicitly cast these types
if needsUsingClause(oldType, newType) {
if needsUsing {
sql := fmt.Sprintf("ALTER TABLE %s ALTER COLUMN %s TYPE %s USING %s::%s;",
qualifiedTableName, cd.New.Name, newType, cd.New.Name, newType)
statements = append(statements, sql)
Expand All @@ -62,17 +63,17 @@ func (cd *ColumnDiff) generateColumnSQL(tableSchema, tableName string, targetSch
}

// Handle default value changes
// If we already dropped the default due to type change, we need to re-add it if there's a new default
// Otherwise, handle default changes normally
if hasTypeChange && hasOldDefault {
// When USING clause was needed, we dropped the default above, so re-add it if there's a new default
// When USING clause was NOT needed, handle default changes normally
if needsUsing && hasOldDefault {
// Default was dropped above; add new default if specified
if newDefault != nil && *newDefault != "" {
sql := fmt.Sprintf("ALTER TABLE %s ALTER COLUMN %s SET DEFAULT %s;",
qualifiedTableName, cd.New.Name, *newDefault)
statements = append(statements, sql)
}
} else {
// Normal default value change handling (no type change involved)
// Normal default value change handling (no USING clause involved)
if (oldDefault == nil) != (newDefault == nil) ||
(oldDefault != nil && newDefault != nil && *oldDefault != *newDefault) {

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