Add method to alter table column

column.go

@@ -34,9 +34,22 @@ const (
 	Time ColumnType = "TIME"
 )
 
+// AlterColumnMode enum.
+type AlterColumnMode uint16
+
+const (
+	// AlterColumnType operation.
+	AlterColumnType AlterColumnMode = iota + 1
+	// AlterColumnRequired operation.
+	AlterColumnRequired
+	// AlterColumnDefault operation.
+	AlterColumnDefault
+)
+
 // Column definition.
 type Column struct {
 	Op        SchemaOp
+	AlterMode AlterColumnMode
 	Name      string
 	Type      ColumnType
 	Rename    string
@@ -75,6 +88,39 @@ func renameColumn(name string, newName string, options []ColumnOption) Column {
 	return column
 }
 
+func alterColumnType(name string, typ ColumnType, options []ColumnOption) []Column {
+	column := Column{
+		Op:        SchemaAlter,
+		Name:      name,
+		Type:      typ,
+		AlterMode: AlterColumnType,
+	}
+	for _, option := range options {
+		if option.isConstraint() {
+			continue
+		}
+		option.applyColumn(&column)
+	}
+
+	return append([]Column{column}, alterColumn(name, options)...)
+}
+
+func alterColumn(name string, options []ColumnOption) []Column {
+	columns := make([]Column, 0, len(options))
+	for _, option := range options {
+		if !option.isConstraint() {
+			continue
+		}
+		column := Column{
+			Op:   SchemaAlter,
+			Name: name,
+		}
+		option.applyColumn(&column)
+		columns = append(columns, column)
+	}
+	return columns
+}
+
 func dropColumn(name string, options []ColumnOption) Column {
 	column := Column{
 		Op:   SchemaDrop,

column_test.go

@@ -65,6 +65,32 @@ func TestRenameColumn(t *testing.T) {
 	}, column)
 }
 
+func TestAlterColumn(t *testing.T) {
+	var (
+		options = []ColumnOption{
+			Required(true),
+			Limit(1000),
+		}
+		columns = alterColumnType("alter", String, options)
+	)
+
+	assert.Equal(t, []Column{
+		{
+			Op:        SchemaAlter,
+			AlterMode: AlterColumnType,
+			Type:      String,
+			Name:      "alter",
+			Limit:     1000,
+		},
+		{
+			Op:        SchemaAlter,
+			AlterMode: AlterColumnRequired,
+			Name:      "alter",
+			Required:  true,
+		},
+	}, columns)
+}
+
 func TestDropColumn(t *testing.T) {
 	var (
 		options = []ColumnOption{

query.go

@@ -16,9 +16,7 @@ type QueryPopulator interface {
 
 // Build for given table using given queriers.
 func Build(table string, queriers ...Querier) Query {
-	var (
-		query = newQuery()
-	)
+	query := newQuery()
 
 	if len(queriers) > 0 {
 		_, query.empty = queriers[0].(Query)
@@ -255,9 +253,7 @@ func (q Query) Sort(fields ...string) Query {
 
 // SortAsc query.
 func (q Query) SortAsc(fields ...string) Query {
-	var (
-		offset = len(q.SortQuery)
-	)
+	offset := len(q.SortQuery)
 
 	q.SortQuery = append(q.SortQuery, make([]SortQuery, len(fields))...)
 	for i := range fields {
@@ -269,9 +265,7 @@ func (q Query) SortAsc(fields ...string) Query {
 
 // SortDesc query.
 func (q Query) SortDesc(fields ...string) Query {
-	var (
-		offset = len(q.SortQuery)
-	)
+	offset := len(q.SortQuery)
 
 	q.SortQuery = append(q.SortQuery, make([]SortQuery, len(fields))...)
 	for i := range fields {
@@ -538,6 +532,10 @@ func (l Limit) applyColumn(column *Column) {
 	column.Limit = int(l)
 }
 
+func (l Limit) isConstraint() bool {
+	return false
+}
+
 // Lock query.
 // This query will be ignored if used outside of transaction.
 type Lock string

schema.go

@@ -81,6 +81,31 @@ func (s *Schema) AddColumn(table string, name string, typ ColumnType, options ..
 	s.add(at.Table)
 }
 
+// AlterColumnType with name.
+//
+// Allows also changing other constraints like [rel.Default] and [rel.Required].
+//
+// WARNING: Not supported by SQLite driver.
+func (s *Schema) AlterColumnType(table string, name string, typ ColumnType, options ...ColumnOption) {
+	at := alterTable(table, nil)
+	at.AlterColumnType(name, typ, options...)
+	s.add(at.Table)
+}
+
+// AlterColumn with name.
+//
+// Only [rel.Default] and [rel.Required] are supported.
+// Support for underlying drivers might wary. For example PostgreSQL supports both,
+// while Microsoft SQL Server and MySQL/MariaDB only supports [rel.Default].
+// See [Schema.AlterColumnType] if other constraints need to be changed also.
+//
+// WARNING: Not supported by SQLite driver.
+func (s *Schema) AlterColumn(table string, name string, options ...ColumnOption) {
+	at := alterTable(table, nil)
+	at.AlterColumn(name, options...)
+	s.add(at.Table)
+}
+
 // RenameColumn by name.
 func (s *Schema) RenameColumn(table string, name string, newName string, options ...ColumnOption) {
 	at := alterTable(table, nil)

schema_options.go

@@ -16,6 +16,7 @@ func applyTableOptions(table *Table, options []TableOption) {
 // Available options are: Nil, Unsigned, Limit, Precision, Scale, Default, Comment, Options.
 type ColumnOption interface {
 	applyColumn(column *Column)
+	isConstraint() bool
 }
 
 func applyColumnOptions(column *Column, options []ColumnOption) {
@@ -43,13 +44,21 @@ func (r Primary) applyColumn(column *Column) {
 	column.Primary = bool(r)
 }
 
+func (r Primary) isConstraint() bool {
+	return false
+}
+
 // Unique set column as unique.
 type Unique bool
 
 func (r Unique) applyColumn(column *Column) {
 	column.Unique = bool(r)
 }
 
+func (r Unique) isConstraint() bool {
+	return false
+}
+
 func (r Unique) applyIndex(index *Index) {
 	index.Unique = bool(r)
 }
@@ -59,6 +68,13 @@ type Required bool
 
 func (r Required) applyColumn(column *Column) {
 	column.Required = bool(r)
+	if column.Op == SchemaAlter {
+		column.AlterMode = AlterColumnRequired
+	}
+}
+
+func (r Required) isConstraint() bool {
+	return true
 }
 
 // Unsigned sets integer column to be unsigned.
@@ -68,26 +84,45 @@ func (u Unsigned) applyColumn(column *Column) {
 	column.Unsigned = bool(u)
 }
 
+func (r Unsigned) isConstraint() bool {
+	return false
+}
+
 // Precision defines the precision for the decimal fields, representing the total number of digits in the number.
 type Precision int
 
 func (p Precision) applyColumn(column *Column) {
 	column.Precision = int(p)
 }
 
+func (p Precision) isConstraint() bool {
+	return false
+}
+
 // Scale Defines the scale for the decimal fields, representing the number of digits after the decimal point.
 type Scale int
 
 func (s Scale) applyColumn(column *Column) {
 	column.Scale = int(s)
 }
 
+func (s Scale) isConstraint() bool {
+	return false
+}
+
 type defaultValue struct {
 	value any
 }
 
 func (d defaultValue) applyColumn(column *Column) {
 	column.Default = d.value
+	if column.Op == SchemaAlter {
+		column.AlterMode = AlterColumnDefault
+	}
+}
+
+func (d defaultValue) isConstraint() bool {
+	return true
 }
 
 // Default allows to set a default value on the column.).
@@ -120,6 +155,10 @@ func (o Options) applyColumn(column *Column) {
 	column.Options = string(o)
 }
 
+func (o Options) isConstraint() bool {
+	return false
+}
+
 func (o Options) applyIndex(index *Index) {
 	index.Options = string(o)
 }

schema_test.go

@@ -118,6 +118,49 @@ func TestSchema_AddColumn(t *testing.T) {
 	}, schema.Migrations[0])
 }
 
+func TestSchema_AlterColumnTypeString(t *testing.T) {
+	var schema Schema
+
+	schema.AlterColumnType("products", "description", String, Limit(100), Unique(false), Primary(false))
+
+	assert.Equal(t, Table{
+		Op:   SchemaAlter,
+		Name: "products",
+		Definitions: []TableDefinition{
+			Column{Name: "description", Type: String, Op: SchemaAlter, Limit: 100, AlterMode: AlterColumnType},
+		},
+	}, schema.Migrations[0])
+}
+
+func TestSchema_AlterColumnTypeNumber(t *testing.T) {
+	var schema Schema
+
+	schema.AlterColumnType("products", "description", Decimal, Scale(10), Precision(2), Unsigned(true), Options(""))
+
+	assert.Equal(t, Table{
+		Op:   SchemaAlter,
+		Name: "products",
+		Definitions: []TableDefinition{
+			Column{Name: "description", Type: Decimal, Op: SchemaAlter, Scale: 10, Precision: 2, Unsigned: true, AlterMode: AlterColumnType},
+		},
+	}, schema.Migrations[0])
+}
+
+func TestSchema_AlterColumn(t *testing.T) {
+	var schema Schema
+
+	schema.AlterColumn("products", "description", Required(true), Default("<no description>"))
+
+	assert.Equal(t, Table{
+		Op:   SchemaAlter,
+		Name: "products",
+		Definitions: []TableDefinition{
+			Column{Name: "description", Op: SchemaAlter, Required: true, AlterMode: AlterColumnRequired},
+			Column{Name: "description", Op: SchemaAlter, Default: "<no description>", AlterMode: AlterColumnDefault},
+		},
+	}, schema.Migrations[0])
+}
+
 func TestSchema_RenameColumn(t *testing.T) {
 	var schema Schema
 
@@ -218,9 +261,7 @@ func TestRaw_InternalTableDefinition(t *testing.T) {
 }
 
 func TestDo(t *testing.T) {
-	var (
-		schema Schema
-	)
+	var schema Schema
 
 	schema.Do(func(ctx context.Context, repo Repository) error { return nil })
 	assert.NotNil(t, schema.Migrations[0])

table.go

@@ -136,6 +136,22 @@ func (at *AlterTable) RenameColumn(name string, newName string, options ...Colum
 	at.Definitions = append(at.Definitions, renameColumn(name, newName, options))
 }
 
+// AlterColumnType with name.
+func (at *AlterTable) AlterColumnType(name string, typ ColumnType, options ...ColumnOption) {
+	defs := alterColumnType(name, typ, options)
+	for _, def := range defs {
+		at.Definitions = append(at.Definitions, def)
+	}
+}
+
+// AlterColumn with name.
+func (at *AlterTable) AlterColumn(name string, options ...ColumnOption) {
+	defs := alterColumn(name, options)
+	for _, def := range defs {
+		at.Definitions = append(at.Definitions, def)
+	}
+}
+
 // DropColumn from this table.
 func (at *AlterTable) DropColumn(name string, options ...ColumnOption) {
 	at.Definitions = append(at.Definitions, dropColumn(name, options))