*: fix issue of multi-schema change with foreign key

ddl/ddl_api.go

@@ -3264,6 +3264,14 @@ func (d *ddl) AlterTable(ctx context.Context, sctx sessionctx.Context, stmt *ast
 			return dbterror.ErrOptOnCacheTable.GenWithStackByArgs("Alter Table")
 		}
 	}
+	// set name for anonymous foreign key.
+	maxForeignKeyID := tb.Meta().MaxForeignKeyID
+	for _, spec := range validSpecs {
+		if spec.Tp == ast.AlterTableAddConstraint && spec.Constraint.Tp == ast.ConstraintForeignKey && spec.Constraint.Name == "" {
+			maxForeignKeyID++
+			spec.Constraint.Name = fmt.Sprintf("fk_%d", maxForeignKeyID)
+		}
+	}
 
 	if len(validSpecs) > 1 {
 		sctx.GetSessionVars().StmtCtx.MultiSchemaInfo = model.NewMultiSchemaInfo()

ddl/fktest/foreign_key_test.go

@@ -1544,3 +1544,32 @@ func getLatestSchemaDiff(t *testing.T, tk *testkit.TestKit) *model.SchemaDiff {
 	require.NoError(t, err)
 	return diff
 }
+
+func TestTestMultiSchemaAddForeignKey(t *testing.T) {
+	store, _ := testkit.CreateMockStoreAndDomain(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("set @@foreign_key_checks=1;")
+	tk.MustExec("use test")
+	tk.MustExec("create table t1 (id int key);")
+	tk.MustExec("create table t2 (a int, b int);")
+	tk.MustExec("alter table t2 add foreign key (a) references t1(id), add foreign key (b) references t1(id)")
+	tk.MustExec("alter table t2 add column c int, add column d int")
+	tk.MustExec("alter table t2 add foreign key (c) references t1(id), add foreign key (d) references t1(id), add index(c), add index(d)")
+	tk.MustExec("drop table t2")
+	tk.MustExec("create table t2 (a int, b int, index idx1(a), index idx2(b));")
+	tk.MustGetErrMsg("alter table t2 drop index idx1, drop index idx2, add foreign key (a) references t1(id), add foreign key (b) references t1(id)",
+		"[ddl:1553]Cannot drop index 'idx1': needed in a foreign key constraint")
+	tk.MustExec("alter table t2 drop index idx1, drop index idx2")
+	tk.MustExec("alter table t2 add foreign key (a) references t1(id), add foreign key (b) references t1(id)")
+	tk.MustQuery("show create table t2").Check(testkit.Rows("t2 CREATE TABLE `t2` (\n" +
+		"  `a` int(11) DEFAULT NULL,\n" +
+		"  `b` int(11) DEFAULT NULL,\n" +
+		"  KEY `fk_1` (`a`),\n" +
+		"  KEY `fk_2` (`b`),\n" +
+		"  CONSTRAINT `fk_1` FOREIGN KEY (`a`) REFERENCES `test`.`t1` (`id`),\n" +
+		"  CONSTRAINT `fk_2` FOREIGN KEY (`b`) REFERENCES `test`.`t1` (`id`)\n" +
+		") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin"))
+	tk.MustExec("drop table t2")
+	tk.MustExec("create table t2 (a int, b int, index idx0(a,b), index idx1(a), index idx2(b));")
+	tk.MustExec("alter table t2 drop index idx1, add foreign key (a) references t1(id), add foreign key (b) references t1(id)")
+}

ddl/multi_schema_change.go

@@ -261,7 +261,10 @@ func fillMultiSchemaInfo(info *model.MultiSchemaInfo, job *model.Job) (err error
 	case model.ActionRebaseAutoID, model.ActionModifyTableComment, model.ActionModifyTableCharsetAndCollate:
 	case model.ActionAddForeignKey:
 		fkInfo := job.Args[0].(*model.FKInfo)
-		info.ForeignKeys = append(info.ForeignKeys, fkInfo.Name)
+		info.AddForeignKeys = append(info.AddForeignKeys, model.AddForeignKeyInfo{
+			Name: fkInfo.Name,
+			Cols: fkInfo.Cols,
+		})
 	default:
 		return dbterror.ErrRunMultiSchemaChanges.FastGenByArgs(job.Type.String())
 	}
@@ -323,6 +326,41 @@ func checkOperateSameColAndIdx(info *model.MultiSchemaInfo) error {
 	return checkIndexes(info.AlterIndexes, true)
 }
 
+func checkOperateDropIndexUseByForeignKey(info *model.MultiSchemaInfo, t table.Table) error {
+	var remainIndexes, droppingIndexes []*model.IndexInfo
+	tbInfo := t.Meta()
+	for _, idx := range tbInfo.Indices {
+		dropping := false
+		for _, name := range info.DropIndexes {
+			if name.L == idx.Name.L {
+				dropping = true
+				break
+			}
+		}
+		if dropping {
+			droppingIndexes = append(droppingIndexes, idx)
+		} else {
+			remainIndexes = append(remainIndexes, idx)
+		}
+	}
+
+	for _, fk := range info.AddForeignKeys {
+		if droppingIdx := findIndexByColumns(tbInfo, droppingIndexes, fk.Cols...); droppingIdx != nil && findIndexByColumns(tbInfo, remainIndexes, fk.Cols...) == nil {
+			return dbterror.ErrDropIndexNeededInForeignKey.GenWithStackByArgs(droppingIdx.Name)
+		}
+	}
+	return nil
+}
+
+func findIndexByColumns(tbInfo *model.TableInfo, indexes []*model.IndexInfo, cols ...model.CIStr) *model.IndexInfo {
+	for _, index := range indexes {
+		if model.IsIndexPrefixCovered(tbInfo, index, cols...) {
+			return index
+		}
+	}
+	return nil
+}
+
 func checkMultiSchemaInfo(info *model.MultiSchemaInfo, t table.Table) error {
 	err := checkOperateSameColAndIdx(info)
 	if err != nil {
@@ -334,6 +372,11 @@ func checkMultiSchemaInfo(info *model.MultiSchemaInfo, t table.Table) error {
 		return err
 	}
 
+	err = checkOperateDropIndexUseByForeignKey(info, t)
+	if err != nil {
+		return err
+	}
+
 	return checkAddColumnTooManyColumns(len(t.Cols()) + len(info.AddColumns) - len(info.DropColumns))
 }
 

parser/model/ddl.go

@@ -316,12 +316,19 @@ type MultiSchemaInfo struct {
 	AddIndexes    []CIStr `json:"-"`
 	DropIndexes   []CIStr `json:"-"`
 	AlterIndexes  []CIStr `json:"-"`
-	ForeignKeys   []CIStr `json:"-"`
+
+	AddForeignKeys []AddForeignKeyInfo `json:"-"`
 
 	RelativeColumns []CIStr `json:"-"`
 	PositionColumns []CIStr `json:"-"`
 }
 
+// AddForeignKeyInfo contains foreign key information.
+type AddForeignKeyInfo struct {
+	Name CIStr
+	Cols []CIStr
+}
+
 // NewMultiSchemaInfo new a MultiSchemaInfo.
 func NewMultiSchemaInfo() *MultiSchemaInfo {
 	return &MultiSchemaInfo{