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feat: Expose prepared statement column and parameter metadata #1743

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14 changes: 5 additions & 9 deletions connection.go
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -224,20 +224,16 @@ func (mc *mysqlConn) Prepare(query string) (driver.Stmt, error) {
columnCount, err := stmt.readPrepareResultPacket()
if err == nil {
if stmt.paramCount > 0 {
if err = mc.skipColumns(stmt.paramCount); err != nil {
// Read parameter metadata instead of skipping it
if stmt.params, err = mc.readColumns(stmt.paramCount, nil); err != nil {
return nil, err
}
}

if columnCount > 0 {
if mc.extCapabilities&clientCacheMetadata != 0 {
if stmt.columns, err = mc.readColumns(int(columnCount), nil); err != nil {
return nil, err
}
} else {
if err = mc.skipColumns(int(columnCount)); err != nil {
return nil, err
}
// Always read column metadata
if stmt.columns, err = mc.readColumns(int(columnCount), stmt.columns); err != nil {
return nil, err
}
}
}
Expand Down
32 changes: 32 additions & 0 deletions fields.go
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -150,6 +150,38 @@ type mysqlField struct {
charSet uint8
}

// FieldMetadata represents metadata about a column or parameter from a prepared statement.
// This is a public struct that exposes the metadata from mysqlField.
type FieldMetadata struct {
// TableName is the name of the table this field belongs to (may be empty for expressions)
TableName string
// Name is the name or alias of the field
Name string
// Length is the maximum length of the field
Length uint32
// Decimals is the number of decimals for numeric types
Decimals byte
// DatabaseTypeName returns the MySQL type name (e.g., "INT", "VARCHAR", "TEXT")
DatabaseTypeName string
// Nullable indicates whether the field can be NULL
Nullable bool
// Unsigned indicates whether a numeric field is unsigned
Unsigned bool
}

// toFieldMetadata converts an internal mysqlField to a public FieldMetadata
func (mf *mysqlField) toFieldMetadata() FieldMetadata {
return FieldMetadata{
TableName: mf.tableName,
Name: mf.name,
Length: mf.length,
Decimals: mf.decimals,
DatabaseTypeName: mf.typeDatabaseName(),
Nullable: mf.flags&flagNotNULL == 0,
Unsigned: mf.flags&flagUnsigned != 0,
}
}

func (mf *mysqlField) scanType() reflect.Type {
switch mf.fieldType {
case fieldTypeTiny:
Expand Down
48 changes: 48 additions & 0 deletions statement.go
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,11 +16,38 @@ import (
"reflect"
)

// StmtMetadata is an interface that provides access to prepared statement metadata.
// It can be used via type assertion on the driver.Stmt returned by Conn.Prepare.
//
// Example usage with database/sql:
//
// conn, _ := db.Conn(ctx)
// conn.Raw(func(driverConn any) error {
// if preparer, ok := driverConn.(driver.ConnPrepareContext); ok {
// stmt, _ := preparer.PrepareContext(ctx, query)
// if meta, ok := stmt.(mysql.StmtMetadata); ok {
// columns := meta.ColumnMetadata()
// params := meta.ParamMetadata()
// }
// }
// return nil
// })
type StmtMetadata interface {
// ColumnMetadata returns metadata about result columns
ColumnMetadata() []FieldMetadata
// ParamMetadata returns metadata about query parameters
ParamMetadata() []FieldMetadata
}

// Verify that mysqlStmt implements StmtMetadata
var _ StmtMetadata = (*mysqlStmt)(nil)

type mysqlStmt struct {
mc *mysqlConn
id uint32
paramCount int
columns []mysqlField
params []mysqlField
}

func (stmt *mysqlStmt) Close() error {
Expand All @@ -42,6 +69,27 @@ func (stmt *mysqlStmt) NumInput() int {
return stmt.paramCount
}

// ColumnMetadata returns metadata about the columns that will be returned by this prepared statement.
// This information is obtained from the MySQL server during the PREPARE phase.
func (stmt *mysqlStmt) ColumnMetadata() []FieldMetadata {
result := make([]FieldMetadata, len(stmt.columns))
for i, col := range stmt.columns {
result[i] = col.toFieldMetadata()
}
return result
}

// ParamMetadata returns metadata about the parameters expected by this prepared statement.
// This information is obtained from the MySQL server during the PREPARE phase.
// Note: MySQL may return limited parameter metadata depending on the query structure.
func (stmt *mysqlStmt) ParamMetadata() []FieldMetadata {
result := make([]FieldMetadata, len(stmt.params))
for i, param := range stmt.params {
result[i] = param.toFieldMetadata()
}
return result
}

func (stmt *mysqlStmt) ColumnConverter(idx int) driver.ValueConverter {
return converter{}
}
Expand Down

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