dialect/sql: add hasneigbors for predicates (#184)

Summary:
Pull Request resolved: https://github.com/facebookincubator/ent/pull/184

This diff is part of the ongoing effort for moving the sql logic out from codegen.

Reviewed By: alexsn

Differential Revision: D18656817

fbshipit-source-id: 71001d37eb78032414c2f83f200d3011b50c114b

dialect/sql/graph.go

@@ -142,3 +142,37 @@ func SetNeighbors(dialect string, s *Step) (q *Selector) {
 	}
 	return q
 }
+
+// HasNeighbors applies on the given Selector a neighbors check.
+func HasNeighbors(q *Selector, s *Step) {
+	builder := Dialect(q.dialect)
+	switch r := s.Edge.Rel; {
+	case r == M2M:
+		pk1 := s.Edge.Columns[1]
+		if s.Edge.Inverse {
+			pk1 = s.Edge.Columns[0]
+		}
+		from := q.Table()
+		join := builder.Table(s.Edge.Table)
+		q.Where(
+			In(
+				from.C(s.From.Column),
+				builder.Select(join.C(pk1)).From(join),
+			),
+		)
+	case r == M2O || (r == O2O && s.Edge.Inverse):
+		from := q.Table()
+		q.Where(NotNull(from.C(s.Edge.Columns[0])))
+	case r == O2M || (r == O2O && !s.Edge.Inverse):
+		from := q.Table()
+		to := builder.Table(s.Edge.Table)
+		q.Where(
+			In(
+				from.C(s.From.Column),
+				builder.Select(to.C(s.Edge.Columns[0])).
+					From(to).
+					Where(NotNull(to.C(s.Edge.Columns[0]))),
+			),
+		)
+	}
+}

dialect/sql/graph_test.go

@@ -311,3 +311,61 @@ JOIN
 		})
 	}
 }
+
+func TestHasNeighbors(t *testing.T) {
+	tests := []struct {
+		name      string
+		step      *Step
+		selector  *Selector
+		wantQuery string
+	}{
+		{
+			name: "O2O/1type",
+			step: func() *Step {
+				// A nodes table; linked-list (next->prev). The "prev"
+				// node holds association pointer. The neighbors query
+				// here checks if a node "has-next".
+				step := &Step{}
+				step.From.V = 1
+				step.From.Table = "nodes"
+				step.From.Column = "id"
+				step.To.Table = "nodes"
+				step.To.Column = "id"
+				step.Edge.Rel = O2O
+				step.Edge.Table = "nodes"
+				step.Edge.Columns = []string{"prev_id"}
+				return step
+			}(),
+			selector:  Select("*").From(Table("nodes")),
+			wantQuery: "SELECT * FROM `nodes` WHERE `nodes`.`id` IN (SELECT `nodes`.`prev_id` FROM `nodes` WHERE `nodes`.`prev_id` IS NOT NULL)",
+		},
+		{
+			name: "O2O/1type/inverse",
+			step: func() *Step {
+				// Same example as above, but the neighbors
+				// query checks if a node "has-previous".
+				step := &Step{}
+				step.From.V = 1
+				step.From.Table = "nodes"
+				step.From.Column = "id"
+				step.To.Table = "nodes"
+				step.To.Column = "id"
+				step.Edge.Rel = O2O
+				step.Edge.Inverse = true
+				step.Edge.Table = "nodes"
+				step.Edge.Columns = []string{"prev_id"}
+				return step
+			}(),
+			selector:  Select("*").From(Table("nodes")),
+			wantQuery: "SELECT * FROM `nodes` WHERE `nodes`.`prev_id` IS NOT NULL",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			HasNeighbors(tt.selector, tt.step)
+			query, args := tt.selector.Query()
+			require.Equal(t, tt.wantQuery, query)
+			require.Empty(t, args)
+		})
+	}
+}