Simplify Batch.Queue for prepared statements

batch.go

@@ -45,9 +45,9 @@ func (b *Batch) Conn() *Conn {
 	return b.conn
 }
 
-// Queue queues a query to batch b. parameterOIDs are required if there are
-// parameters and query is not the name of a prepared statement.
-// resultFormatCodes are required if there is a result.
+// Queue queues a query to batch b. query can be an SQL query or the name of a prepared statement. parameterOIDs and
+// resultFormatCodes should be nil if query is a prepared statement. Otherwise, parameterOIDs are required if there are
+// parameters and resultFormatCodes are required if there is a result.
 func (b *Batch) Queue(query string, arguments []interface{}, parameterOIDs []pgtype.OID, resultFormatCodes []int16) {
 	b.items = append(b.items, &batchItem{
 		query:             query,
@@ -95,7 +95,21 @@ func (b *Batch) Send(ctx context.Context) error {
 		}
 
 		if ps != nil {
-			batch.ExecPrepared(ps.Name, paramValues, paramFormats, bi.resultFormatCodes)
+			resultFormats := bi.resultFormatCodes
+			if resultFormats == nil {
+				resultFormats = make([]int16, len(ps.FieldDescriptions))
+				for i := range resultFormats {
+					if dt, ok := b.conn.ConnInfo.DataTypeForOID(ps.FieldDescriptions[i].DataType); ok {
+						if _, ok := dt.Value.(pgtype.BinaryDecoder); ok {
+							resultFormats[i] = BinaryFormatCode
+						} else {
+							resultFormats[i] = TextFormatCode
+						}
+					}
+				}
+			}
+
+			batch.ExecPrepared(ps.Name, paramValues, paramFormats, resultFormats)
 		} else {
 			oids := make([]uint32, len(parameterOIDs))
 			for i := 0; i < len(parameterOIDs); i++ {

batch_test.go

@@ -177,7 +177,7 @@ func TestConnBeginBatchWithPreparedStatement(t *testing.T) {
 		batch.Queue("ps1",
 			[]interface{}{5},
 			nil,
-			[]int16{pgx.BinaryFormatCode},
+			nil,
 		)
 	}