Merge pull request #656 from upper/allow-select-from-db-result

allow using db.Result as subquery

internal/sqladapter/result.go

@@ -213,7 +213,7 @@ func (r *Result) Select(fields ...interface{}) db.Result {
 
 // String satisfies fmt.Stringer
 func (r *Result) String() string {
-	query, err := r.buildPaginator()
+	query, err := r.Paginator()
 	if err != nil {
 		panic(err.Error())
 	}
@@ -222,7 +222,7 @@ func (r *Result) String() string {
 
 // All dumps all Results into a pointer to an slice of structs or maps.
 func (r *Result) All(dst interface{}) error {
-	query, err := r.buildPaginator()
+	query, err := r.Paginator()
 	if err != nil {
 		r.setErr(err)
 		return err
@@ -235,7 +235,7 @@ func (r *Result) All(dst interface{}) error {
 // One fetches only one Result from the set.
 func (r *Result) One(dst interface{}) error {
 	one := r.Limit(1).(*Result)
-	query, err := one.buildPaginator()
+	query, err := one.Paginator()
 	if err != nil {
 		r.setErr(err)
 		return err
@@ -251,7 +251,7 @@ func (r *Result) Next(dst interface{}) bool {
 	defer r.iterMu.Unlock()
 
 	if r.iter == nil {
-		query, err := r.buildPaginator()
+		query, err := r.Paginator()
 		if err != nil {
 			r.setErr(err)
 			return false
@@ -309,7 +309,7 @@ func (r *Result) Update(values interface{}) error {
 }
 
 func (r *Result) TotalPages() (uint, error) {
-	query, err := r.buildPaginator()
+	query, err := r.Paginator()
 	if err != nil {
 		r.setErr(err)
 		return 0, err
@@ -325,7 +325,7 @@ func (r *Result) TotalPages() (uint, error) {
 }
 
 func (r *Result) TotalEntries() (uint64, error) {
-	query, err := r.buildPaginator()
+	query, err := r.Paginator()
 	if err != nil {
 		r.setErr(err)
 		return 0, err
@@ -391,7 +391,7 @@ func (r *Result) Count() (uint64, error) {
 	return counter.Count, nil
 }
 
-func (r *Result) buildPaginator() (db.Paginator, error) {
+func (r *Result) Paginator() (db.Paginator, error) {
 	if err := r.Err(); err != nil {
 		return nil, err
 	}

internal/sqlbuilder/builder.go

@@ -51,7 +51,11 @@ var defaultMapOptions = MapOptions{
 	IncludeNil:    false,
 }
 
-type compilable interface {
+type hasPaginator interface {
+	Paginator() (db.Paginator, error)
+}
+
+type isCompilable interface {
 	Compile() (string, error)
 	Arguments() []interface{}
 }
@@ -347,7 +351,17 @@ func columnFragments(columns []interface{}) ([]exql.Fragment, []interface{}, err
 
 	for i := range columns {
 		switch v := columns[i].(type) {
-		case compilable:
+		case hasPaginator:
+			p, err := v.Paginator()
+			if err != nil {
+				return nil, nil, err
+			}
+
+			q, a := Preprocess(p.String(), p.Arguments())
+
+			f[i] = exql.RawValue("(" + q + ")")
+			args = append(args, a...)
+		case isCompilable:
 			c, err := v.Compile()
 			if err != nil {
 				return nil, nil, err

internal/sqlbuilder/convert.go

@@ -122,7 +122,13 @@ func preprocessFn(arg interface{}) (string, []interface{}) {
 		switch t := arg.(type) {
 		case *adapter.RawExpr:
 			return Preprocess(t.Raw(), t.Arguments())
-		case compilable:
+		case hasPaginator:
+			p, err := t.Paginator()
+			if err == nil {
+				return `(` + p.String() + `)`, p.Arguments()
+			}
+			panic(err.Error())
+		case isCompilable:
 			c, err := t.Compile()
 			if err == nil {
 				return `(` + c + `)`, t.Arguments()

internal/testsuite/sql_suite.go

@@ -1898,3 +1898,34 @@ func (s *SQLTestSuite) Test_Issue565() {
 	s.Error(err)
 	s.Zero(result.Name)
 }
+
+func (s *SQLTestSuite) TestSelectFromSubquery() {
+	sess := s.Session()
+
+	{
+		var artists []artistType
+		q := sess.SQL().SelectFrom(
+			sess.SQL().SelectFrom("artist").Where(db.Cond{
+				"name": db.IsNotNull(),
+			}),
+		).As("_q")
+		err := q.All(&artists)
+		s.NoError(err)
+
+		s.NotZero(len(artists))
+	}
+
+	{
+		var artists []artistType
+		q := sess.SQL().SelectFrom(
+			sess.Collection("artist").Find(db.Cond{
+				"name": db.IsNotNull(),
+			}),
+		).As("_q")
+		err := q.All(&artists)
+		s.NoError(err)
+
+		s.NotZero(len(artists))
+	}
+
+}