add Pluck function to retrieve a list of column values

engine.go

@@ -1417,6 +1417,16 @@ func (engine *Engine) Find(beans interface{}, condiBeans ...interface{}) error {
 	return session.Find(beans, condiBeans...)
 }
 
+// Pluck retrieve a list of column values.
+// colName is the column name where values from
+// slicePtr should be a slice which will filled by the list values
+// beans is optional which represents the table, should be a *Struct
+func (engine *Engine) Pluck(colName string, slicePtr interface{}, beans ...interface{}) error {
+	session := engine.NewSession()
+	defer session.Close()
+	return session.Pluck(colName, slicePtr, beans...)
+}
+
 // FindAndCount find the results and also return the counts
 func (engine *Engine) FindAndCount(rowsSlicePtr interface{}, condiBean ...interface{}) (int64, error) {
 	session := engine.NewSession()

interface.go

@@ -64,6 +64,7 @@ type Interface interface {
 	Update(bean interface{}, condiBeans ...interface{}) (int64, error)
 	UseBool(...string) *Session
 	Where(interface{}, ...interface{}) *Session
+	Pluck(colName string, slicePtr interface{}, bean ...interface{}) error
 }
 
 // EngineInterface defines the interface which Engine, EngineGroup will implementate.

session_pluck.go

@@ -0,0 +1,61 @@
+package xorm
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// Pluck retrieve a list of column values.
+// colName is the column name where values from
+// slicePtr should be a slice which will filled by the list values
+// beans is optional which represents the table, should be a *Struct
+func (session *Session) Pluck(colName string, slicePtr interface{}, beans ...interface{}) error {
+	if session.isAutoClose {
+		defer session.Close()
+	}
+	return session.pluck(colName, slicePtr, beans...)
+}
+
+func (session *Session) pluck(colName string, slicePtr interface{}, beans ...interface{}) error {
+	sliceValue := reflect.Indirect(reflect.ValueOf(slicePtr))
+	if sliceValue.Kind() != reflect.Slice {
+		return errors.New("needs a pointer to a slice")
+	}
+	sliceElemType := sliceValue.Type().Elem()
+	rows := []map[string]interface{}{}
+	query := session
+	if session.statement.selectStr == "" {
+		query.Select(colName)
+	}
+	if len(beans) != 0 {
+		// find table
+		bean := beans[0]
+		beanValue := reflect.ValueOf(bean)
+		if beanValue.Kind() != reflect.Ptr || beanValue.Elem().Kind() != reflect.Struct {
+			return errors.New("needs a pointer to a struct")
+		}
+		session.statement.setRefValue(beanValue)
+		tbName := session.statement.TableName()
+		query.Table(tbName)
+	}
+	if err := query.Find(&rows); err != nil {
+		return err
+	}
+
+	colSegs := strings.Split(colName, ".")
+	col := colSegs[len(colSegs)-1] // last one
+	col = strings.Trim(col, "`")   // unwrap column name
+	nSlice := reflect.New(sliceValue.Type()).Elem()
+	rowsLen := len(rows)
+	for i := 0; i < rowsLen; i++ {
+		if v, ok := rows[i][col]; !ok {
+			return fmt.Errorf("cannot find column: %s", col)
+		} else {
+			nSlice = reflect.Append(nSlice, reflect.ValueOf(v).Convert(sliceElemType))
+		}
+	}
+	sliceValue.Set(nSlice)
+	return nil
+}

session_pluck_test.go

@@ -0,0 +1,103 @@
+package xorm
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestPluck(t *testing.T) {
+	var err error
+	assert.NoError(t, prepareEngine())
+	assertSync(t, new(Userinfo))
+	_, err = testEngine.Insert([]Userinfo{
+		{
+			Username: "Lenny",
+		},
+		{
+			Username: "Jimmy",
+		},
+		{
+			Username: "John Wick",
+		},
+	})
+	assert.NoError(t, err)
+	var ids []int64
+	err = testEngine.Table("userinfo").Alias("u").Pluck("u.id", &ids)
+	assert.NoError(t, err)
+	t.Logf("%+v", ids)
+
+	err = testEngine.Table("userinfo").Alias("u").Pluck("`u`.`id`", &ids)
+	assert.NoError(t, err)
+	t.Logf("%+v", ids)
+
+	var names []string
+	err = testEngine.Table("userinfo").Pluck("username", &names)
+	assert.NoError(t, err)
+	t.Logf("%+v", names)
+}
+
+func TestPluck2(t *testing.T) {
+	var err error
+	assert.NoError(t, prepareEngine())
+	assertSync(t, new(Userinfo))
+	_, err = testEngine.Insert([]Userinfo{
+		{
+			Username: "Lenny",
+		},
+		{
+			Username: "Jimmy",
+		},
+		{
+			Username: "John Wick",
+		},
+	})
+	assert.NoError(t, err)
+	var names []string
+	err = testEngine.Pluck("username", &names, new(Userinfo))
+	assert.NoError(t, err)
+	t.Logf("%+v", names)
+}
+
+func TestPluck3(t *testing.T) {
+	var err error
+	assert.NoError(t, prepareEngine())
+	assertSync(t, new(Userinfo))
+	_, err = testEngine.Insert([]Userinfo{
+		{
+			Username: "Lenny",
+		},
+		{
+			Username: "Jimmy",
+		},
+		{
+			Username: "John Wick",
+		},
+	})
+	assert.NoError(t, err)
+	var names []string
+	err = testEngine.Table("userinfo").Pluck("username", &names, new(Team))
+	assert.NoError(t, err)
+	t.Logf("%+v", names)
+}
+
+func TestPluck4(t *testing.T) {
+	var err error
+	assert.NoError(t, prepareEngine())
+	assertSync(t, new(Userinfo))
+	_, err = testEngine.Insert([]Userinfo{
+		{
+			Username: "Lenny",
+		},
+		{
+			Username: "Jimmy",
+		},
+		{
+			Username: "John Wick",
+		},
+	})
+	assert.NoError(t, err)
+	var names []string
+	err = testEngine.Table("userinfo").Select("id, username as name").Pluck("name", &names, new(Team))
+	assert.NoError(t, err)
+	t.Logf("%+v", names)
+}