dialect/sqlgraph: initial work for create-node api (#211)

Summary:
Pull Request resolved: https://github.com/facebookincubator/ent/pull/211

Move out the logic from the Go templates to Go code.

Next diff will add the edges of the node.

Reviewed By: alexsn

Differential Revision: D18762049

fbshipit-source-id: c9a93672415a26a6f4a7d466e569b8b0e8b0f9ee

dialect/sql/graph.go

@@ -4,6 +4,17 @@
 
 package sql
 
+import (
+	"context"
+	"database/sql"
+	"database/sql/driver"
+	"encoding/json"
+	"fmt"
+
+	"github.com/facebookincubator/ent/dialect"
+	"github.com/facebookincubator/ent/schema/field"
+)
+
 // Rel is a relation type of an edge.
 type Rel int
 
@@ -262,3 +273,109 @@ func HasNeighborsWith(q *Selector, s *Step, pred func(*Selector)) {
 		q.Where(In(from.C(s.From.Column), matches))
 	}
 }
+
+type (
+	// FieldSpec holds the information for updating a field
+	// column in the database.
+	FieldSpec struct {
+		Column string
+		Type   field.Type
+		Value  driver.Value // value to be stored.
+	}
+
+	// EdgeSpec holds the information for updating a field
+	// column in the database.
+	EdgeSpec struct {
+		Rel     Rel
+		Table   string
+		Columns []string
+		Inverse bool
+		Value   driver.Value
+	}
+
+	// CreateSpec holds the information for creating a node
+	// in the graph.
+	CreateSpec struct {
+		// Type or table name.
+		Table string
+		// ID field.
+		ID *FieldSpec
+		// Fields.
+		Fields []*FieldSpec
+		// Edges.
+		Edges []*EdgeSpec
+	}
+)
+
+// CreateNode applies the spec on the graph.
+func CreateNode(ctx context.Context, drv dialect.Driver, spec *CreateSpec) error {
+	tx, err := drv.Tx(ctx)
+	if err != nil {
+		return err
+	}
+	insert := Dialect(drv.Dialect()).Insert(spec.Table).Default()
+	for _, fi := range spec.Fields {
+		value := fi.Value
+		if fi.Type == field.TypeJSON {
+			if value, err = json.Marshal(value); err != nil {
+				return err
+			}
+		}
+		insert.Set(fi.Column, value)
+	}
+	// ID was provided by the user.
+	if spec.ID.Value != nil {
+		insert.Set(spec.ID.Column, spec.ID.Value)
+		query, args := insert.Query()
+		if err := tx.Exec(ctx, query, args, new(sql.Result)); err != nil {
+			return rollback(tx, err)
+		}
+	} else {
+		id, err := insertLastID(ctx, tx, insert.Returning(spec.ID.Column))
+		if err != nil {
+			return rollback(tx, err)
+		}
+		spec.ID.Value = id
+	}
+	return tx.Commit()
+}
+
+// insertLastID invokes the insert query on the transaction and returns the LastInsertID.
+func insertLastID(ctx context.Context, tx dialect.ExecQuerier, insert *InsertBuilder) (int64, error) {
+	query, args := insert.Query()
+	// PostgreSQL does not support the LastInsertId() method of sql.Result
+	// on Exec, and should be extracted manually using the `RETURNING` clause.
+	if insert.Dialect() == dialect.Postgres {
+		rows := &sql.Rows{}
+		if err := tx.Query(ctx, query, args, rows); err != nil {
+			return 0, err
+		}
+		defer rows.Close()
+		if !rows.Next() {
+			return 0, fmt.Errorf("no rows found for query: %v", query)
+		}
+		var id int64
+		if err := rows.Scan(&id); err != nil {
+			return 0, err
+		}
+		return id, nil
+	}
+	// MySQL, SQLite, etc.
+	var res sql.Result
+	if err := tx.Exec(ctx, query, args, &res); err != nil {
+		return 0, err
+	}
+	id, err := res.LastInsertId()
+	if err != nil {
+		return 0, err
+	}
+	return id, nil
+}
+
+// rollback calls to tx.Rollback and wraps the given error with the rollback error if occurred.
+func rollback(tx dialect.Tx, err error) error {
+	if rerr := tx.Rollback(); rerr != nil {
+		err = fmt.Errorf("%s: %v", err.Error(), rerr)
+	}
+	return err
+}