Add field tag to ignore migration (#4028)

* Add field tag to ignore migration

* Fix null value with space

* refactor migration tag

.gitignore

@@ -2,3 +2,4 @@ TODO*
 documents
 coverage.txt
 _book
+.idea

migrator/migrator.go

@@ -396,7 +396,7 @@ func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnTy
 		}
 	}
 
-	if alterColumn {
+	if alterColumn && !field.IgnoreMigration {
 		return m.DB.Migrator().AlterColumn(value, field.Name)
 	}
 

schema/field.go

@@ -70,6 +70,7 @@ type Field struct {
 	ReflectValueOf         func(reflect.Value) reflect.Value
 	ValueOf                func(reflect.Value) (value interface{}, zero bool)
 	Set                    func(reflect.Value, interface{}) error
+	IgnoreMigration        bool
 }
 
 func (schema *Schema) ParseField(fieldStruct reflect.StructField) *Field {
@@ -189,6 +190,7 @@ func (schema *Schema) ParseField(fieldStruct reflect.StructField) *Field {
 	}
 
 	// default value is function or null or blank (primary keys)
+	field.DefaultValue = strings.TrimSpace(field.DefaultValue)
 	skipParseDefaultValue := strings.Contains(field.DefaultValue, "(") &&
 		strings.Contains(field.DefaultValue, ")") || strings.ToLower(field.DefaultValue) == "null" || field.DefaultValue == ""
 	switch reflect.Indirect(fieldValue).Kind() {
@@ -295,11 +297,23 @@ func (schema *Schema) ParseField(fieldStruct reflect.StructField) *Field {
 	}
 
 	// setup permission
-	if _, ok := field.TagSettings["-"]; ok {
+	if val, ok := field.TagSettings["-"]; ok {
+		val = strings.ToLower(strings.TrimSpace(val))
+		switch val {
+		case "-":
 			field.Creatable = false
 			field.Updatable = false
 			field.Readable = false
 			field.DataType = ""
+		case "all":
+			field.Creatable = false
+			field.Updatable = false
+			field.Readable = false
+			field.DataType = ""
+			field.IgnoreMigration = true
+		case "migration":
+			field.IgnoreMigration = true
+		}
 	}
 
 	if v, ok := field.TagSettings["->"]; ok {

tests/migrate_test.go

@@ -66,6 +66,7 @@ func TestSmartMigrateColumn(t *testing.T) {
 		Name                string    `gorm:"size:128"`
 		Salary              float64   `gorm:"precision:2"`
 		Birthday            time.Time `gorm:"precision:2"`
+		NameIgnoreMigration string    `gorm:"size:100"`
 	}
 
 	if err := DB.Table("user_migrate_columns").AutoMigrate(&UserMigrateColumn2{}); err != nil {
@@ -99,6 +100,7 @@ func TestSmartMigrateColumn(t *testing.T) {
 		Name                string    `gorm:"size:256"`
 		Salary              float64   `gorm:"precision:3"`
 		Birthday            time.Time `gorm:"precision:3"`
+		NameIgnoreMigration string    `gorm:"size:128;-:migration"`
 	}
 
 	if err := DB.Table("user_migrate_columns").AutoMigrate(&UserMigrateColumn3{}); err != nil {
@@ -124,6 +126,10 @@ func TestSmartMigrateColumn(t *testing.T) {
 			if precision, _, _ := columnType.DecimalSize(); (fullSupported || precision != 0) && precision != 3 {
 				t.Fatalf("birthday's precision should be 2, but got %v", precision)
 			}
+		case "name_ignore_migration":
+			if length, _ := columnType.Length(); (fullSupported || length != 0) && length != 100 {
+				t.Fatalf("name_ignore_migration's length should still be 100 but got %v", length)
+			}
 		}
 	}