Move db related basic functions to models/db (#17075)

* Move db related basic functions to models/db

* Fix lint

* Fix lint

* Fix test

* Fix lint

* Fix lint

* revert unnecessary change

* Fix test

* Fix wrong replace string

* Use *Context

* Correct committer spelling and fix wrong replaced words

Co-authored-by: zeripath <art27@cantab.net>

models/db/context.go

@@ -0,0 +1,86 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package db
+
+import (
+	"code.gitea.io/gitea/modules/setting"
+
+	"xorm.io/builder"
+	"xorm.io/xorm"
+)
+
+// Context represents a db context
+type Context struct {
+	e Engine
+}
+
+// Engine returns db engine
+func (ctx *Context) Engine() Engine {
+	return ctx.e
+}
+
+// NewSession returns a new session
+func (ctx *Context) NewSession() *xorm.Session {
+	e, ok := ctx.e.(*xorm.Engine)
+	if ok {
+		return e.NewSession()
+	}
+	return nil
+}
+
+// DefaultContext represents a Context with default Engine
+func DefaultContext() *Context {
+	return &Context{x}
+}
+
+// Committer represents an interface to Commit or Close the Context
+type Committer interface {
+	Commit() error
+	Close() error
+}
+
+// TxContext represents a transaction Context
+func TxContext() (*Context, Committer, error) {
+	sess := x.NewSession()
+	if err := sess.Begin(); err != nil {
+		sess.Close()
+		return nil, nil, err
+	}
+
+	return &Context{sess}, sess, nil
+}
+
+// WithContext represents executing database operations
+func WithContext(f func(ctx *Context) error) error {
+	return f(&Context{x})
+}
+
+// WithTx represents executing database operations on a transaction
+func WithTx(f func(ctx *Context) error) error {
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	if err := f(&Context{sess}); err != nil {
+		return err
+	}
+
+	return sess.Commit()
+}
+
+// Iterate iterates the databases and doing something
+func Iterate(ctx *Context, tableBean interface{}, cond builder.Cond, fun func(idx int, bean interface{}) error) error {
+	return ctx.e.Where(cond).
+		BufferSize(setting.Database.IterateBufferSize).
+		Iterate(tableBean, fun)
+}
+
+// Insert inserts records into database
+func Insert(ctx *Context, beans ...interface{}) error {
+	_, err := ctx.e.Insert(beans...)
+	return err
+}