dialect/sql/schema: add postgres table and column builders

Summary: Pull Request resolved: https://github.com/facebookincubator/ent/pull/114

Reviewed By: alexsn

Differential Revision: D18059082

fbshipit-source-id: fffec25143fa5f2a0ed2c79787abacefad724862

dialect/sql/schema/postgres.go

@@ -227,6 +227,19 @@ func (d *Postgres) scanColumn(c *Column, rows *sql.Rows) error {
 	}
 }
 
+// tBuilder returns the TableBuilder for the given table.
+func (d *Postgres) tBuilder(t *Table) *sql.TableBuilder {
+	b := sql.Dialect(dialect.Postgres).
+		CreateTable(t.Name).IfNotExists()
+	for _, c := range t.Columns {
+		b.Column(d.cBuilder(c))
+	}
+	for _, pk := range t.PrimaryKey {
+		b.PrimaryKey(pk.Name)
+	}
+	return b
+}
+
 // cType returns the PostgreSQL string type for this column.
 func (d *Postgres) cType(c *Column) (t string) {
 	switch c.Type {
@@ -262,3 +275,16 @@ func (d *Postgres) cType(c *Column) (t string) {
 	}
 	return t
 }
+
+// cBuilder returns the ColumnBuilder for the given column.
+func (d *Postgres) cBuilder(c *Column) *sql.ColumnBuilder {
+	b := sql.Dialect(dialect.Postgres).
+		Column(c.Name).Type(d.cType(c)).Attr(c.Attr)
+	c.unique(b)
+	if c.Increment {
+		b.Attr("GENERATED BY DEFAULT AS IDENTITY")
+	}
+	c.nullable(b)
+	c.defaultValue(b)
+	return b
+}