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rows.go
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81 lines (70 loc) · 2.19 KB
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package sqlx
import (
"database/sql"
"errors"
"fmt"
"github.com/tietang/sqlx/reflectx"
"reflect"
)
type rowsi interface {
Close() error
Columns() ([]string, error)
Err() error
Next() bool
Scan(...interface{}) error
}
// Rows is a wrapper around sql.Rows which caches costly reflect operations
// during a looped StructScan
type Rows struct {
*sql.Rows
unsafe bool
Mapper *reflectx.Mapper
// these fields cache memory use for a rows during iteration w/ structScan
started bool
fields [][]int
values []interface{}
}
// SliceScan using this Rows.
func (r *Rows) SliceScan() ([]interface{}, error) {
return SliceScan(r)
}
// MapScan using this Rows.
func (r *Rows) MapScan(dest map[string]interface{}) error {
return MapScan(r, dest)
}
// StructScan is like sql.Rows.Scan, but scans a single Row into a single Struct.
// Use this and iterate over Rows manually when the memory load of Select() might be
// prohibitive. *Rows.StructScan caches the reflect work of matching up column
// positions to fields to avoid that overhead per scan, which means it is not safe
// to run StructScan on the same Rows instance with different struct types.
func (r *Rows) StructScan(dest interface{}) error {
v := reflect.ValueOf(dest)
if v.Kind() != reflect.Ptr {
return errors.New("must pass a pointer, not a value, to StructScan destination")
}
v = v.Elem()
if !r.started {
columns, err := r.Columns()
if err != nil {
return err
}
m := r.Mapper
r.fields = m.TraversalsByName(v.Type(), columns)
// if we are not unsafe and are missing fields, return an error
if f, err := missingFields(r.fields); err != nil && !r.unsafe {
return fmt.Errorf("missing destination name %s in %T", columns[f], dest)
}
r.values = make([]interface{}, len(columns))
r.started = true
}
err := fieldsByTraversal(v, r.fields, r.values, true)
if err != nil {
return err
}
// scan into the struct field pointers and append to our results
err = r.Scan(r.values...)
if err != nil {
return err
}
return r.Err()
}