refactor: distinguish between Unique and UniqueIndex (#6386)

* refactor: distinguish between UniqueIndex and Index

* add test

* add ParseIndex test

* modify unique to constraint

* modify unique to constraint

* fix MigrateColumnUnique

* fix test

* fix unit test

* update test mod

* add MigrateColumnUnique to Migrator interface

* fix format lint

* add comment

* go mod tidy

* revert: revert MigrateColumn

* resolve conflicts

migrator/migrator.go

@@ -110,15 +110,20 @@ func (m Migrator) FullDataTypeOf(field *schema.Field) (expr clause.Expr) {
 	return
 }
 
+func (m Migrator) GetQueryAndExecTx() (queryTx, execTx *gorm.DB) {
+	queryTx = m.DB.Session(&gorm.Session{})
+	execTx = queryTx
+	if m.DB.DryRun {
+		queryTx.DryRun = false
+		execTx = m.DB.Session(&gorm.Session{Logger: &printSQLLogger{Interface: m.DB.Logger}})
+	}
+	return queryTx, execTx
+}
+
 // AutoMigrate auto migrate values
 func (m Migrator) AutoMigrate(values ...interface{}) error {
 	for _, value := range m.ReorderModels(values, true) {
-		queryTx := m.DB.Session(&gorm.Session{})
+		queryTx, execTx := m.GetQueryAndExecTx()
-		execTx := queryTx
-		if m.DB.DryRun {
-			queryTx.DryRun = false
-			execTx = m.DB.Session(&gorm.Session{Logger: &printSQLLogger{Interface: m.DB.Logger}})
-		}
 		if !queryTx.Migrator().HasTable(value) {
 			if err := execTx.Migrator().CreateTable(value); err != nil {
 				return err
@@ -268,7 +273,7 @@ func (m Migrator) CreateTable(values ...interface{}) error {
 					}
 					if constraint := rel.ParseConstraint(); constraint != nil {
 						if constraint.Schema == stmt.Schema {
-							sql, vars := buildConstraint(constraint)
+							sql, vars := constraint.Build()
 							createTableSQL += sql + ","
 							values = append(values, vars...)
 						}
@@ -276,6 +281,11 @@ func (m Migrator) CreateTable(values ...interface{}) error {
 				}
 			}
 
+			for _, uni := range stmt.Schema.ParseUniqueConstraints() {
+				createTableSQL += "CONSTRAINT ? UNIQUE (?),"
+				values = append(values, clause.Column{Name: uni.Name}, clause.Expr{SQL: stmt.Quote(uni.Field.DBName)})
+			}
+
 			for _, chk := range stmt.Schema.ParseCheckConstraints() {
 				createTableSQL += "CONSTRAINT ? CHECK (?),"
 				values = append(values, clause.Column{Name: chk.Name}, clause.Expr{SQL: chk.Constraint})
@@ -439,6 +449,10 @@ func (m Migrator) RenameColumn(value interface{}, oldName, newName string) error
 
 // MigrateColumn migrate column
 func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnType gorm.ColumnType) error {
+	if field.IgnoreMigration {
+		return nil
+	}
+
 	// found, smart migrate
 	fullDataType := strings.TrimSpace(strings.ToLower(m.DB.Migrator().FullDataTypeOf(field).SQL))
 	realDataType := strings.ToLower(columnType.DatabaseTypeName())
@@ -499,7 +513,7 @@ func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnTy
 	}
 
 	// check unique
-	if unique, ok := columnType.Unique(); ok && unique != field.Unique {
+	if unique, ok := columnType.Unique(); ok && unique != (field.Unique || field.UniqueIndex != "") {
 		// not primary key
 		if !field.PrimaryKey {
 			alterColumn = true
@@ -630,37 +644,36 @@ func (m Migrator) DropView(name string) error {
 	return m.DB.Exec("DROP VIEW IF EXISTS ?", clause.Table{Name: name}).Error
 }
 
-func buildConstraint(constraint *schema.Constraint) (sql string, results []interface{}) {
+// GuessConstraintAndTable guess statement's constraint and it's table based on name
-	sql = "CONSTRAINT ? FOREIGN KEY ? REFERENCES ??"
+//
-	if constraint.OnDelete != "" {
+// Deprecated: use GuessConstraintInterfaceAndTable instead.
-		sql += " ON DELETE " + constraint.OnDelete
+func (m Migrator) GuessConstraintAndTable(stmt *gorm.Statement, name string) (*schema.Constraint, *schema.CheckConstraint, string) {
+	constraint, table := m.GuessConstraintInterfaceAndTable(stmt, name)
+	switch c := constraint.(type) {
+	case *schema.Constraint:
+		return c, nil, table
+	case *schema.CheckConstraint:
+		return nil, c, table
+	default:
+		return nil, nil, table
 	}
-
-	if constraint.OnUpdate != "" {
-		sql += " ON UPDATE " + constraint.OnUpdate
-	}
-
-	var foreignKeys, references []interface{}
-	for _, field := range constraint.ForeignKeys {
-		foreignKeys = append(foreignKeys, clause.Column{Name: field.DBName})
-	}
-
-	for _, field := range constraint.References {
-		references = append(references, clause.Column{Name: field.DBName})
-	}
-	results = append(results, clause.Table{Name: constraint.Name}, foreignKeys, clause.Table{Name: constraint.ReferenceSchema.Table}, references)
-	return
 }
 
-// GuessConstraintAndTable guess statement's constraint and it's table based on name
+// GuessConstraintInterfaceAndTable guess statement's constraint and it's table based on name
-func (m Migrator) GuessConstraintAndTable(stmt *gorm.Statement, name string) (_ *schema.Constraint, _ *schema.Check, table string) {
+// nolint:cyclop
+func (m Migrator) GuessConstraintInterfaceAndTable(stmt *gorm.Statement, name string) (_ schema.ConstraintInterface, table string) {
 	if stmt.Schema == nil {
-		return nil, nil, stmt.Table
+		return nil, stmt.Table
 	}
 
 	checkConstraints := stmt.Schema.ParseCheckConstraints()
 	if chk, ok := checkConstraints[name]; ok {
-		return nil, &chk, stmt.Table
+		return &chk, stmt.Table
+	}
+
+	uniqueConstraints := stmt.Schema.ParseUniqueConstraints()
+	if uni, ok := uniqueConstraints[name]; ok {
+		return &uni, stmt.Table
 	}
 
 	getTable := func(rel *schema.Relationship) string {
@@ -675,7 +688,7 @@ func (m Migrator) GuessConstraintAndTable(stmt *gorm.Statement, name string) (_
 
 	for _, rel := range stmt.Schema.Relationships.Relations {
 		if constraint := rel.ParseConstraint(); constraint != nil && constraint.Name == name {
-			return constraint, nil, getTable(rel)
+			return constraint, getTable(rel)
 		}
 	}
 
@@ -683,40 +696,39 @@ func (m Migrator) GuessConstraintAndTable(stmt *gorm.Statement, name string) (_
 		for k := range checkConstraints {
 			if checkConstraints[k].Field == field {
 				v := checkConstraints[k]
-				return nil, &v, stmt.Table
+				return &v, stmt.Table
+			}
+		}
+
+		for k := range uniqueConstraints {
+			if uniqueConstraints[k].Field == field {
+				v := uniqueConstraints[k]
+				return &v, stmt.Table
 			}
 		}
 
 		for _, rel := range stmt.Schema.Relationships.Relations {
 			if constraint := rel.ParseConstraint(); constraint != nil && rel.Field == field {
-				return constraint, nil, getTable(rel)
+				return constraint, getTable(rel)
 			}
 		}
 	}
 
-	return nil, nil, stmt.Schema.Table
+	return nil, stmt.Schema.Table
 }
 
 // CreateConstraint create constraint
 func (m Migrator) CreateConstraint(value interface{}, name string) error {
 	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
-		constraint, chk, table := m.GuessConstraintAndTable(stmt, name)
+		constraint, table := m.GuessConstraintInterfaceAndTable(stmt, name)
-		if chk != nil {
-			return m.DB.Exec(
-				"ALTER TABLE ? ADD CONSTRAINT ? CHECK (?)",
-				m.CurrentTable(stmt), clause.Column{Name: chk.Name}, clause.Expr{SQL: chk.Constraint},
-			).Error
-		}
-
 		if constraint != nil {
 			vars := []interface{}{clause.Table{Name: table}}
 			if stmt.TableExpr != nil {
 				vars[0] = stmt.TableExpr
 			}
-			sql, values := buildConstraint(constraint)
+			sql, values := constraint.Build()
 			return m.DB.Exec("ALTER TABLE ? ADD "+sql, append(vars, values...)...).Error
 		}
-
 		return nil
 	})
 }
@@ -724,11 +736,9 @@ func (m Migrator) CreateConstraint(value interface{}, name string) error {
 // DropConstraint drop constraint
 func (m Migrator) DropConstraint(value interface{}, name string) error {
 	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
-		constraint, chk, table := m.GuessConstraintAndTable(stmt, name)
+		constraint, table := m.GuessConstraintInterfaceAndTable(stmt, name)
 		if constraint != nil {
-			name = constraint.Name
+			name = constraint.GetName()
-		} else if chk != nil {
-			name = chk.Name
 		}
 		return m.DB.Exec("ALTER TABLE ? DROP CONSTRAINT ?", clause.Table{Name: table}, clause.Column{Name: name}).Error
 	})
@@ -739,11 +749,9 @@ func (m Migrator) HasConstraint(value interface{}, name string) bool {
 	var count int64
 	m.RunWithValue(value, func(stmt *gorm.Statement) error {
 		currentDatabase := m.DB.Migrator().CurrentDatabase()
-		constraint, chk, table := m.GuessConstraintAndTable(stmt, name)
+		constraint, table := m.GuessConstraintInterfaceAndTable(stmt, name)
 		if constraint != nil {
-			name = constraint.Name
+			name = constraint.GetName()
-		} else if chk != nil {
-			name = chk.Name
 		}
 
 		return m.DB.Raw(

schema/check.go

@@ -1,35 +0,0 @@
-package schema
-
-import (
-	"regexp"
-	"strings"
-)
-
-// reg match english letters and midline
-var regEnLetterAndMidline = regexp.MustCompile("^[A-Za-z-_]+$")
-
-type Check struct {
-	Name       string
-	Constraint string // length(phone) >= 10
-	*Field
-}
-
-// ParseCheckConstraints parse schema check constraints
-func (schema *Schema) ParseCheckConstraints() map[string]Check {
-	checks := map[string]Check{}
-	for _, field := range schema.FieldsByDBName {
-		if chk := field.TagSettings["CHECK"]; chk != "" {
-			names := strings.Split(chk, ",")
-			if len(names) > 1 && regEnLetterAndMidline.MatchString(names[0]) {
-				checks[names[0]] = Check{Name: names[0], Constraint: strings.Join(names[1:], ","), Field: field}
-			} else {
-				if names[0] == "" {
-					chk = strings.Join(names[1:], ",")
-				}
-				name := schema.namer.CheckerName(schema.Table, field.DBName)
-				checks[name] = Check{Name: name, Constraint: chk, Field: field}
-			}
-		}
-	}
-	return checks
-}

schema/constraint.go

@@ -0,0 +1,66 @@
+package schema
+
+import (
+	"regexp"
+	"strings"
+
+	"gorm.io/gorm/clause"
+)
+
+// reg match english letters and midline
+var regEnLetterAndMidline = regexp.MustCompile("^[A-Za-z-_]+$")
+
+type CheckConstraint struct {
+	Name       string
+	Constraint string // length(phone) >= 10
+	*Field
+}
+
+func (chk *CheckConstraint) GetName() string { return chk.Name }
+
+func (chk *CheckConstraint) Build() (sql string, vars []interface{}) {
+	return "CONSTRAINT ? CHECK (?)", []interface{}{clause.Column{Name: chk.Name}, clause.Expr{SQL: chk.Constraint}}
+}
+
+// ParseCheckConstraints parse schema check constraints
+func (schema *Schema) ParseCheckConstraints() map[string]CheckConstraint {
+	checks := map[string]CheckConstraint{}
+	for _, field := range schema.FieldsByDBName {
+		if chk := field.TagSettings["CHECK"]; chk != "" {
+			names := strings.Split(chk, ",")
+			if len(names) > 1 && regEnLetterAndMidline.MatchString(names[0]) {
+				checks[names[0]] = CheckConstraint{Name: names[0], Constraint: strings.Join(names[1:], ","), Field: field}
+			} else {
+				if names[0] == "" {
+					chk = strings.Join(names[1:], ",")
+				}
+				name := schema.namer.CheckerName(schema.Table, field.DBName)
+				checks[name] = CheckConstraint{Name: name, Constraint: chk, Field: field}
+			}
+		}
+	}
+	return checks
+}
+
+type UniqueConstraint struct {
+	Name  string
+	Field *Field
+}
+
+func (uni *UniqueConstraint) GetName() string { return uni.Name }
+
+func (uni *UniqueConstraint) Build() (sql string, vars []interface{}) {
+	return "CONSTRAINT ? UNIQUE (?)", []interface{}{clause.Column{Name: uni.Name}, clause.Column{Name: uni.Field.DBName}}
+}
+
+// ParseUniqueConstraints parse schema unique constraints
+func (schema *Schema) ParseUniqueConstraints() map[string]UniqueConstraint {
+	uniques := make(map[string]UniqueConstraint)
+	for _, field := range schema.Fields {
+		if field.Unique {
+			name := schema.namer.UniqueName(schema.Table, field.DBName)
+			uniques[name] = UniqueConstraint{Name: name, Field: field}
+		}
+	}
+	return uniques
+}

schema/constraint_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"gorm.io/gorm/schema"
+	"gorm.io/gorm/utils/tests"
 )
 
 type UserCheck struct {
@@ -20,7 +21,7 @@ func TestParseCheck(t *testing.T) {
 		t.Fatalf("failed to parse user check, got error %v", err)
 	}
 
-	results := map[string]schema.Check{
+	results := map[string]schema.CheckConstraint{
 		"name_checker": {
 			Name:       "name_checker",
 			Constraint: "name <> 'jinzhu'",
@@ -53,3 +54,31 @@ func TestParseCheck(t *testing.T) {
 		}
 	}
 }
+
+func TestParseUniqueConstraints(t *testing.T) {
+	type UserUnique struct {
+		Name1 string `gorm:"unique"`
+		Name2 string `gorm:"uniqueIndex"`
+	}
+
+	user, err := schema.Parse(&UserUnique{}, &sync.Map{}, schema.NamingStrategy{})
+	if err != nil {
+		t.Fatalf("failed to parse user unique, got error %v", err)
+	}
+	constraints := user.ParseUniqueConstraints()
+
+	results := map[string]schema.UniqueConstraint{
+		"uni_user_uniques_name1": {
+			Name:  "uni_user_uniques_name1",
+			Field: &schema.Field{Name: "Name1", Unique: true},
+		},
+	}
+	for k, result := range results {
+		v, ok := constraints[k]
+		if !ok {
+			t.Errorf("Failed to found unique constraint %v from parsed constraints %+v", k, constraints)
+		}
+		tests.AssertObjEqual(t, result, v, "Name")
+		tests.AssertObjEqual(t, result.Field, v.Field, "Name", "Unique", "UniqueIndex")
+	}
+}

schema/field.go

@@ -89,6 +89,12 @@ type Field struct {
 	Set                    func(context.Context, reflect.Value, interface{}) error
 	Serializer             SerializerInterface
 	NewValuePool           FieldNewValuePool
+
+	// In some db (e.g. MySQL), Unique and UniqueIndex are indistinguishable.
+	// When a column has a (not Mul) UniqueIndex, Migrator always reports its gorm.ColumnType is Unique.
+	// It causes field unnecessarily migration.
+	// Therefore, we need to record the UniqueIndex on this column (exclude Mul UniqueIndex) for MigrateColumnUnique.
+	UniqueIndex string
 }
 
 func (field *Field) BindName() string {

schema/index.go

@@ -13,8 +13,8 @@ type Index struct {
 	Type    string // btree, hash, gist, spgist, gin, and brin
 	Where   string
 	Comment string
-	Option  string // WITH PARSER parser_name
+	Option  string        // WITH PARSER parser_name
-	Fields  []IndexOption
+	Fields  []IndexOption // Note: IndexOption's Field maybe the same
 }
 
 type IndexOption struct {
@@ -67,7 +67,7 @@ func (schema *Schema) ParseIndexes() map[string]Index {
 	}
 	for _, index := range indexes {
 		if index.Class == "UNIQUE" && len(index.Fields) == 1 {
-			index.Fields[0].Field.Unique = true
+			index.Fields[0].Field.UniqueIndex = index.Name
 		}
 	}
 	return indexes

schema/index_test.go

@@ -1,11 +1,11 @@
 package schema_test
 
 import (
-	"reflect"
 	"sync"
 	"testing"
 
 	"gorm.io/gorm/schema"
+	"gorm.io/gorm/utils/tests"
 )
 
 type UserIndex struct {
@@ -19,6 +19,7 @@ type UserIndex struct {
 	OID          int64  `gorm:"index:idx_id;index:idx_oid,unique"`
 	MemberNumber string `gorm:"index:idx_id,priority:1"`
 	Name7        string `gorm:"index:type"`
+	Name8        string `gorm:"index:,length:10;index:,collate:utf8"`
 
 	// Composite Index: Flattened structure.
 	Data0A string `gorm:"index:,composite:comp_id0"`
@@ -65,7 +66,7 @@ func TestParseIndex(t *testing.T) {
 		"idx_name": {
 			Name:   "idx_name",
 			Class:  "UNIQUE",
-			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "Name2", Unique: true}}},
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "Name2", UniqueIndex: "idx_name"}}},
 		},
 		"idx_user_indices_name3": {
 			Name:  "idx_user_indices_name3",
@@ -81,7 +82,7 @@ func TestParseIndex(t *testing.T) {
 		"idx_user_indices_name4": {
 			Name:   "idx_user_indices_name4",
 			Class:  "UNIQUE",
-			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "Name4", Unique: true}}},
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "Name4", UniqueIndex: "idx_user_indices_name4"}}},
 		},
 		"idx_user_indices_name5": {
 			Name:    "idx_user_indices_name5",
@@ -102,18 +103,27 @@ func TestParseIndex(t *testing.T) {
 		},
 		"idx_id": {
 			Name:   "idx_id",
-			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "MemberNumber"}}, {Field: &schema.Field{Name: "OID", Unique: true}}},
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "MemberNumber"}}, {Field: &schema.Field{Name: "OID", UniqueIndex: "idx_oid"}}},
 		},
 		"idx_oid": {
 			Name:   "idx_oid",
 			Class:  "UNIQUE",
-			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "OID", Unique: true}}},
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "OID", UniqueIndex: "idx_oid"}}},
 		},
 		"type": {
 			Name:   "type",
 			Type:   "",
 			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "Name7"}}},
 		},
+		"idx_user_indices_name8": {
+			Name: "idx_user_indices_name8",
+			Type: "",
+			Fields: []schema.IndexOption{
+				{Field: &schema.Field{Name: "Name8"}, Length: 10},
+				// Note: Duplicate Columns
+				{Field: &schema.Field{Name: "Name8"}, Collate: "utf8"},
+			},
+		},
 		"idx_user_indices_comp_id0": {
 			Name: "idx_user_indices_comp_id0",
 			Type: "",
@@ -146,40 +156,109 @@ func TestParseIndex(t *testing.T) {
 		},
 	}
 
-	indices := user.ParseIndexes()
+	CheckIndices(t, results, user.ParseIndexes())
+}
 
-	for k, result := range results {
+func TestParseIndexWithUniqueIndexAndUnique(t *testing.T) {
-		v, ok := indices[k]
+	type IndexTest struct {
-		if !ok {
+		FieldA string `gorm:"unique;index"` // unique and index
-			t.Fatalf("Failed to found index %v from parsed indices %+v", k, indices)
+		FieldB string `gorm:"unique"`       // unique
-		}
 
-		for _, name := range []string{"Name", "Class", "Type", "Where", "Comment", "Option"} {
+		FieldC string `gorm:"index:,unique"`     // uniqueIndex
-			if reflect.ValueOf(result).FieldByName(name).Interface() != reflect.ValueOf(v).FieldByName(name).Interface() {
+		FieldD string `gorm:"uniqueIndex;index"` // uniqueIndex and index
-				t.Errorf(
-					"index %v %v should equal, expects %v, got %v",
-					k, name, reflect.ValueOf(result).FieldByName(name).Interface(), reflect.ValueOf(v).FieldByName(name).Interface(),
-				)
-			}
-		}
 
-		for idx, ef := range result.Fields {
+		FieldE1 string `gorm:"uniqueIndex:uniq_field_e1_e2"` // mul uniqueIndex
-			rf := v.Fields[idx]
+		FieldE2 string `gorm:"uniqueIndex:uniq_field_e1_e2"`
-			if rf.Field.Name != ef.Field.Name {
-				t.Fatalf("index field should equal, expects %v, got %v", rf.Field.Name, ef.Field.Name)
-			}
-			if rf.Field.Unique != ef.Field.Unique {
-				t.Fatalf("index field '%s' should equal, expects %v, got %v", rf.Field.Name, rf.Field.Unique, ef.Field.Unique)
-			}
 
-			for _, name := range []string{"Expression", "Sort", "Collate", "Length"} {
+		FieldF1 string `gorm:"uniqueIndex:uniq_field_f1_f2;index"` // mul uniqueIndex and index
-				if reflect.ValueOf(ef).FieldByName(name).Interface() != reflect.ValueOf(rf).FieldByName(name).Interface() {
+		FieldF2 string `gorm:"uniqueIndex:uniq_field_f1_f2;"`
-					t.Errorf(
+
-						"index %v field #%v's %v should equal, expects %v, got %v", k, idx+1, name,
+		FieldG string `gorm:"unique;uniqueIndex"` // unique and uniqueIndex
-						reflect.ValueOf(ef).FieldByName(name).Interface(), reflect.ValueOf(rf).FieldByName(name).Interface(),
+
-					)
+		FieldH1 string `gorm:"unique;uniqueIndex:uniq_field_h1_h2"` // unique and mul uniqueIndex
-				}
+		FieldH2 string `gorm:"uniqueIndex:uniq_field_h1_h2"`        // unique and mul uniqueIndex
+	}
+	indexSchema, err := schema.Parse(&IndexTest{}, &sync.Map{}, schema.NamingStrategy{})
+	if err != nil {
+		t.Fatalf("failed to parse user index, got error %v", err)
+	}
+	indices := indexSchema.ParseIndexes()
+	CheckIndices(t, map[string]schema.Index{
+		"idx_index_tests_field_a": {
+			Name:   "idx_index_tests_field_a",
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "FieldA", Unique: true}}},
+		},
+		"idx_index_tests_field_c": {
+			Name:   "idx_index_tests_field_c",
+			Class:  "UNIQUE",
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "FieldC", UniqueIndex: "idx_index_tests_field_c"}}},
+		},
+		"idx_index_tests_field_d": {
+			Name:  "idx_index_tests_field_d",
+			Class: "UNIQUE",
+			Fields: []schema.IndexOption{
+				{Field: &schema.Field{Name: "FieldD"}},
+				// Note: Duplicate Columns
+				{Field: &schema.Field{Name: "FieldD"}},
+			},
+		},
+		"uniq_field_e1_e2": {
+			Name:  "uniq_field_e1_e2",
+			Class: "UNIQUE",
+			Fields: []schema.IndexOption{
+				{Field: &schema.Field{Name: "FieldE1"}},
+				{Field: &schema.Field{Name: "FieldE2"}},
+			},
+		},
+		"idx_index_tests_field_f1": {
+			Name:   "idx_index_tests_field_f1",
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "FieldF1"}}},
+		},
+		"uniq_field_f1_f2": {
+			Name:  "uniq_field_f1_f2",
+			Class: "UNIQUE",
+			Fields: []schema.IndexOption{
+				{Field: &schema.Field{Name: "FieldF1"}},
+				{Field: &schema.Field{Name: "FieldF2"}},
+			},
+		},
+		"idx_index_tests_field_g": {
+			Name:   "idx_index_tests_field_g",
+			Class:  "UNIQUE",
+			Fields: []schema.IndexOption{{Field: &schema.Field{Name: "FieldG", Unique: true, UniqueIndex: "idx_index_tests_field_g"}}},
+		},
+		"uniq_field_h1_h2": {
+			Name:  "uniq_field_h1_h2",
+			Class: "UNIQUE",
+			Fields: []schema.IndexOption{
+				{Field: &schema.Field{Name: "FieldH1", Unique: true}},
+				{Field: &schema.Field{Name: "FieldH2"}},
+			},
+		},
+	}, indices)
+}
+
+func CheckIndices(t *testing.T, expected, actual map[string]schema.Index) {
+	for k, ei := range expected {
+		t.Run(k, func(t *testing.T) {
+			ai, ok := actual[k]
+			if !ok {
+				t.Errorf("expected index %q but actual missing", k)
+				return
 			}
-		}
+			tests.AssertObjEqual(t, ai, ei, "Name", "Class", "Type", "Where", "Comment", "Option")
+			if len(ei.Fields) != len(ai.Fields) {
+				t.Errorf("expected index %q field length is %d but actual %d", k, len(ei.Fields), len(ai.Fields))
+				return
+			}
+			for i, ef := range ei.Fields {
+				af := ai.Fields[i]
+				tests.AssertObjEqual(t, af, ef, "Name", "Unique", "UniqueIndex", "Expression", "Sort", "Collate", "Length")
+			}
+		})
+		delete(actual, k)
+	}
+	for k := range actual {
+		t.Errorf("unexpected index %q", k)
 	}
 }

schema/interfaces.go

@@ -4,6 +4,12 @@ import (
 	"gorm.io/gorm/clause"
 )
 
+// ConstraintInterface database constraint interface
+type ConstraintInterface interface {
+	GetName() string
+	Build() (sql string, vars []interface{})
+}
+
 // GormDataTypeInterface gorm data type interface
 type GormDataTypeInterface interface {
 	GormDataType() string

schema/relationship.go

@@ -605,6 +605,7 @@ func (schema *Schema) guessRelation(relation *Relationship, field *Field, cgl gu
 	}
 }
 
+// Constraint is ForeignKey Constraint
 type Constraint struct {
 	Name            string
 	Field           *Field
@@ -616,6 +617,31 @@ type Constraint struct {
 	OnUpdate        string
 }
 
+func (constraint *Constraint) GetName() string { return constraint.Name }
+
+func (constraint *Constraint) Build() (sql string, vars []interface{}) {
+	sql = "CONSTRAINT ? FOREIGN KEY ? REFERENCES ??"
+	if constraint.OnDelete != "" {
+		sql += " ON DELETE " + constraint.OnDelete
+	}
+
+	if constraint.OnUpdate != "" {
+		sql += " ON UPDATE " + constraint.OnUpdate
+	}
+
+	foreignKeys := make([]interface{}, 0, len(constraint.ForeignKeys))
+	for _, field := range constraint.ForeignKeys {
+		foreignKeys = append(foreignKeys, clause.Column{Name: field.DBName})
+	}
+
+	references := make([]interface{}, 0, len(constraint.References))
+	for _, field := range constraint.References {
+		references = append(references, clause.Column{Name: field.DBName})
+	}
+	vars = append(vars, clause.Table{Name: constraint.Name}, foreignKeys, clause.Table{Name: constraint.ReferenceSchema.Table}, references)
+	return
+}
+
 func (rel *Relationship) ParseConstraint() *Constraint {
 	str := rel.Field.TagSettings["CONSTRAINT"]
 	if str == "-" {