Handle syntax to specify an index prefix length (#2399)

Handle syntax to specify an index prefix length

dialect.go

@@ -48,6 +48,9 @@ type Dialect interface {
 	// BuildKeyName returns a valid key name (foreign key, index key) for the given table, field and reference
 	BuildKeyName(kind, tableName string, fields ...string) string
 
+	// NormalizeIndexAndColumn returns valid index name and column name depending on each dialect
+	NormalizeIndexAndColumn(indexName, columnName string) (string, string)
+
 	// CurrentDatabase return current database name
 	CurrentDatabase() string
 }

dialect_common.go

@@ -9,6 +9,8 @@ import (
 	"time"
 )
 
+var keyNameRegex = regexp.MustCompile("[^a-zA-Z0-9]+")
+
 // DefaultForeignKeyNamer contains the default foreign key name generator method
 type DefaultForeignKeyNamer struct {
 }
@@ -166,10 +168,15 @@ func (commonDialect) DefaultValueStr() string {
 // BuildKeyName returns a valid key name (foreign key, index key) for the given table, field and reference
 func (DefaultForeignKeyNamer) BuildKeyName(kind, tableName string, fields ...string) string {
 	keyName := fmt.Sprintf("%s_%s_%s", kind, tableName, strings.Join(fields, "_"))
-	keyName = regexp.MustCompile("[^a-zA-Z0-9]+").ReplaceAllString(keyName, "_")
+	keyName = keyNameRegex.ReplaceAllString(keyName, "_")
 	return keyName
 }
 
+// NormalizeIndexAndColumn returns argument's index name and column name without doing anything
+func (commonDialect) NormalizeIndexAndColumn(indexName, columnName string) (string, string) {
+	return indexName, columnName
+}
+
 // IsByteArrayOrSlice returns true of the reflected value is an array or slice
 func IsByteArrayOrSlice(value reflect.Value) bool {
 	return (value.Kind() == reflect.Array || value.Kind() == reflect.Slice) && value.Type().Elem() == reflect.TypeOf(uint8(0))

dialect_mysql.go

@@ -11,6 +11,8 @@ import (
 	"unicode/utf8"
 )
 
+var mysqlIndexRegex = regexp.MustCompile(`^(.+)\((\d+)\)$`)
+
 type mysql struct {
 	commonDialect
 }
@@ -178,7 +180,7 @@ func (s mysql) BuildKeyName(kind, tableName string, fields ...string) string {
 	bs := h.Sum(nil)
 
 	// sha1 is 40 characters, keep first 24 characters of destination
-	destRunes := []rune(regexp.MustCompile("[^a-zA-Z0-9]+").ReplaceAllString(fields[0], "_"))
+	destRunes := []rune(keyNameRegex.ReplaceAllString(fields[0], "_"))
 	if len(destRunes) > 24 {
 		destRunes = destRunes[:24]
 	}
@@ -186,6 +188,17 @@ func (s mysql) BuildKeyName(kind, tableName string, fields ...string) string {
 	return fmt.Sprintf("%s%x", string(destRunes), bs)
 }
 
+// NormalizeIndexAndColumn returns index name and column name for specify an index prefix length if needed
+func (mysql) NormalizeIndexAndColumn(indexName, columnName string) (string, string) {
+	submatch := mysqlIndexRegex.FindStringSubmatch(indexName)
+	if len(submatch) != 3 {
+		return indexName, columnName
+	}
+	indexName = submatch[1]
+	columnName = fmt.Sprintf("%s(%s)", columnName, submatch[2])
+	return indexName, columnName
+}
+
 func (mysql) DefaultValueStr() string {
 	return "VALUES()"
 }

dialects/mssql/mssql.go

@@ -198,6 +198,11 @@ func (mssql) DefaultValueStr() string {
 	return "DEFAULT VALUES"
 }
 
+// NormalizeIndexAndColumn returns argument's index name and column name without doing anything
+func (mssql) NormalizeIndexAndColumn(indexName, columnName string) (string, string) {
+	return indexName, columnName
+}
+
 func currentDatabaseAndTable(dialect gorm.Dialect, tableName string) (string, string) {
 	if strings.Contains(tableName, ".") {
 		splitStrings := strings.SplitN(tableName, ".", 2)

migration_test.go

@@ -538,3 +538,42 @@ func TestModifyColumnType(t *testing.T) {
 		t.Errorf("No error should happen when ModifyColumn, but got %v", err)
 	}
 }
+
+func TestIndexWithPrefixLength(t *testing.T) {
+	if dialect := os.Getenv("GORM_DIALECT"); dialect != "mysql" {
+		t.Skip("Skipping this because only mysql support setting an index prefix length")
+	}
+
+	type IndexWithPrefix struct {
+		gorm.Model
+		Name        string
+		Description string `gorm:"type:text;index:idx_index_with_prefixes_length(100)"`
+	}
+	type IndexesWithPrefix struct {
+		gorm.Model
+		Name         string
+		Description1 string `gorm:"type:text;index:idx_index_with_prefixes_length(100)"`
+		Description2 string `gorm:"type:text;index:idx_index_with_prefixes_length(100)"`
+	}
+	type IndexesWithPrefixAndWithoutPrefix struct {
+		gorm.Model
+		Name        string `gorm:"index:idx_index_with_prefixes_length"`
+		Description string `gorm:"type:text;index:idx_index_with_prefixes_length(100)"`
+	}
+	tables := []interface{}{&IndexWithPrefix{}, &IndexesWithPrefix{}, &IndexesWithPrefixAndWithoutPrefix{}}
+	for _, table := range tables {
+		scope := DB.NewScope(table)
+		tableName := scope.TableName()
+		t.Run(fmt.Sprintf("Create index with prefix length: %s", tableName), func(t *testing.T) {
+			if err := DB.DropTableIfExists(table).Error; err != nil {
+				t.Errorf("Failed to drop %s table: %v", tableName, err)
+			}
+			if err := DB.CreateTable(table).Error; err != nil {
+				t.Errorf("Failed to create %s table: %v", tableName, err)
+			}
+			if !scope.Dialect().HasIndex(tableName, "idx_index_with_prefixes_length") {
+				t.Errorf("Failed to create %s table index:", tableName)
+			}
+		})
+	}
+}

scope.go

@@ -1284,7 +1284,8 @@ func (scope *Scope) autoIndex() *Scope {
 				if name == "INDEX" || name == "" {
 					name = scope.Dialect().BuildKeyName("idx", scope.TableName(), field.DBName)
 				}
-				indexes[name] = append(indexes[name], field.DBName)
+				name, column := scope.Dialect().NormalizeIndexAndColumn(name, field.DBName)
+				indexes[name] = append(indexes[name], column)
 			}
 		}
 
@@ -1295,7 +1296,8 @@ func (scope *Scope) autoIndex() *Scope {
 				if name == "UNIQUE_INDEX" || name == "" {
 					name = scope.Dialect().BuildKeyName("uix", scope.TableName(), field.DBName)
 				}
-				uniqueIndexes[name] = append(uniqueIndexes[name], field.DBName)
+				name, column := scope.Dialect().NormalizeIndexAndColumn(name, field.DBName)
+				uniqueIndexes[name] = append(uniqueIndexes[name], column)
 			}
 		}
 	}