Added support for supplying the fields to query in the select statement

Example usage: 'NewUserQuerySet(db).Select(UserDBSchema.Name, UserDBSchema.Email).All(&users)'
This will fetch only the 'name' and 'email' fields for all users,
instead of fetching all the fields in the table.

internal/queryset/generator/generator.go

@@ -56,6 +56,7 @@ func (g Generator) writeQuerySetsToOutput(r io.Reader, packageName, outFile stri
 import (
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/jinzhu/gorm"

internal/queryset/generator/queryset_test.go

@@ -112,6 +112,8 @@ type testQueryFunc func(t *testing.T, m sqlmock.Sqlmock, db *gorm.DB)
 func TestQueries(t *testing.T) {
 	funcs := []testQueryFunc{
 		testUserSelectAll,
+		testUserSelectAllSingleField,
+		testUserSelectAllMultipleFields,
 		testUserSelectWithLimitAndOffset,
 		testUserSelectAllNoRecords,
 		testUserSelectOne,
@@ -152,6 +154,26 @@ func testUserSelectAll(t *testing.T, m sqlmock.Sqlmock, db *gorm.DB) {
 	assert.Equal(t, expUsers, users)
 }
 
+func testUserSelectAllSingleField(t *testing.T, m sqlmock.Sqlmock, db *gorm.DB) {
+	expUsers := getTestUsers(2)
+	m.ExpectQuery(fixedFullRe("SELECT name FROM `users` WHERE `users`.`deleted_at` IS NULL")).
+		WillReturnRows(getRowsForUsers(expUsers))
+
+	var users []test.User
+	assert.Nil(t, test.NewUserQuerySet(db).Select(test.UserDBSchema.Name).All(&users))
+	assert.Equal(t, expUsers, users)
+}
+
+func testUserSelectAllMultipleFields(t *testing.T, m sqlmock.Sqlmock, db *gorm.DB) {
+	expUsers := getTestUsers(2)
+	m.ExpectQuery(fixedFullRe("SELECT name,email FROM `users` WHERE `users`.`deleted_at` IS NULL")).
+		WillReturnRows(getRowsForUsers(expUsers))
+
+	var users []test.User
+	assert.Nil(t, test.NewUserQuerySet(db).Select(test.UserDBSchema.Name, test.UserDBSchema.Email).All(&users))
+	assert.Equal(t, expUsers, users)
+}
+
 func testUserSelectWithLimitAndOffset(t *testing.T, m sqlmock.Sqlmock, db *gorm.DB) {
 	expUsers := getTestUsers(2)
 	req := "SELECT * FROM `users` WHERE `users`.`deleted_at` IS NULL LIMIT 1 OFFSET 1"

internal/queryset/generator/template.go

@@ -13,6 +13,7 @@ const qsCode = `
 // ===== BEGIN of all query sets
 
 {{ range .Configs }}
+  {{ $ft := printf "%s%s" .StructName "DBSchemaField" }}
   // ===== BEGIN of query set {{ .Name }}
 
 	// {{ .Name }} is an queryset type for {{ .StructName }}
@@ -31,6 +32,15 @@ const qsCode = `
 	  return New{{ .Name }}(db)
   }
 
+	func (qs {{ .Name }}) Select(fields ...{{ $ft }}) {{ .Name }} {
+	names := []string{}
+	for _, f := range fields {
+		names = append(names, f.String())
+	}
+
+	return qs.w(qs.db.Select(strings.Join(names, ",")))
+}
+
 	{{ range .Methods }}
 		{{ .GetDoc .GetMethodName }}
 		func ({{ .GetReceiverDeclaration }}) {{ .GetMethodName }}({{ .GetArgsDeclaration }})
@@ -43,7 +53,6 @@ const qsCode = `
 
 	// ===== BEGIN of {{ .StructName }} modifiers
 
-	{{ $ft := printf "%s%s" .StructName "DBSchemaField" }}
 	// {{ $ft }} describes database schema field. It requires for method 'Update'
 	type {{ $ft }} string