fix: checks for error after rows.Next call (#480)

dialect/sql/scan.go

@@ -17,6 +17,7 @@ type ColumnScanner interface {
 	Next() bool
 	Scan(...interface{}) error
 	Columns() ([]string, error)
+	Err() error
 }
 
 // ScanOne scans one row to the given value. It fails if the rows holds more than 1 row.
@@ -29,6 +30,9 @@ func ScanOne(rows ColumnScanner, v interface{}) error {
 		return fmt.Errorf("sql/scan: unexpected number of columns: %d", n)
 	}
 	if !rows.Next() {
+		if rows.Err() != nil {
+			return rows.Err()
+		}
 		return sql.ErrNoRows
 	}
 	if err := rows.Scan(v); err != nil {
@@ -37,7 +41,7 @@ func ScanOne(rows ColumnScanner, v interface{}) error {
 	if rows.Next() {
 		return fmt.Errorf("sql/scan: expect exactly one row in result set")
 	}
-	return nil
+	return rows.Err()
 }
 
 // ScanInt64 scans and returns an int64 from the rows columns.
@@ -92,7 +96,7 @@ func ScanSlice(rows ColumnScanner, v interface{}) error {
 		vv := reflect.Append(rv, scan.value(values...))
 		rv.Set(vv)
 	}
-	return nil
+	return rows.Err()
 }
 
 // rowScan is the configuration for scanning one sql.Row.

dialect/sql/schema/mysql.go

@@ -31,6 +31,9 @@ func (d *MySQL) init(ctx context.Context, tx dialect.Tx) error {
 	}
 	defer rows.Close()
 	if !rows.Next() {
+		if rows.Err() != nil {
+			return rows.Err()
+		}
 		return fmt.Errorf("mysql: version variable was not found")
 	}
 	version := make([]string, 2)
@@ -75,6 +78,9 @@ func (d *MySQL) table(ctx context.Context, tx dialect.Tx, name string) (*Table,
 		}
 		t.AddColumn(c)
 	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
 	if err := rows.Close(); err != nil {
 		return nil, fmt.Errorf("mysql: closing rows %v", err)
 	}
@@ -426,6 +432,9 @@ func (d *MySQL) scanIndexes(rows *sql.Rows) (Indexes, error) {
 		}
 		idx.columns = append(idx.columns, column)
 	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
 	return i, nil
 }
 

dialect/sql/schema/postgres.go

@@ -29,6 +29,9 @@ func (d *Postgres) init(ctx context.Context, tx dialect.Tx) error {
 	}
 	defer rows.Close()
 	if !rows.Next() {
+		if rows.Err() != nil {
+			return rows.Err()
+		}
 		return fmt.Errorf("server_version_num variable was not found")
 	}
 	var version string
@@ -93,6 +96,9 @@ func (d *Postgres) table(ctx context.Context, tx dialect.Tx, name string) (*Tabl
 		}
 		t.AddColumn(c)
 	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
 	if err := rows.Close(); err != nil {
 		return nil, fmt.Errorf("closing rows %v", err)
 	}
@@ -184,6 +190,9 @@ func (d *Postgres) indexes(ctx context.Context, tx dialect.Tx, table string) (In
 		}
 		idx.columns = append(idx.columns, column)
 	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
 	return idxs, nil
 }
 

dialect/sql/schema/sqlite.go

@@ -168,6 +168,9 @@ func (d *SQLite) table(ctx context.Context, tx dialect.Tx, name string) (*Table,
 		}
 		t.AddColumn(c)
 	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
 	if err := rows.Close(); err != nil {
 		return nil, fmt.Errorf("sqlite: closing rows %v", err)
 	}
@@ -215,6 +218,9 @@ func (d *SQLite) indexes(ctx context.Context, tx dialect.Tx, name string) (Index
 		i.primary = origin.String == "pk"
 		idx = append(idx, i)
 	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
 	if err := rows.Close(); err != nil {
 		return nil, fmt.Errorf("closing rows %v", err)
 	}

dialect/sql/sqlgraph/graph.go

@@ -516,7 +516,7 @@ func QueryEdges(ctx context.Context, drv dialect.Driver, spec *EdgeQuerySpec) er
 			return err
 		}
 	}
-	return nil
+	return rows.Err()
 }
 
 type query struct {
@@ -540,7 +540,7 @@ func (q *query) nodes(ctx context.Context, drv dialect.Driver) error {
 			return err
 		}
 	}
-	return nil
+	return rows.Err()
 }
 
 func (q *query) count(ctx context.Context, drv dialect.Driver) (int, error) {
@@ -723,6 +723,9 @@ func (u *updater) setTableColumns(update *sql.UpdateBuilder, addEdges, clearEdge
 func (u *updater) scan(rows *sql.Rows) error {
 	defer rows.Close()
 	if !rows.Next() {
+		if rows.Err() != nil {
+			return rows.Err()
+		}
 		return &NotFoundError{table: u.Node.Table, id: u.Node.ID.Value}
 	}
 	if err := rows.Scan(u.ScanValues...); err != nil {