efcore 新特性 SaveChanges Events

Intro

昨天早上看到之前關注的一個 efcore 的 issue 被 closed ，于是看了一眼， ef core 新合并了一個 PR，在 DbContext 中增加了 SaveChanges 相關的幾個事件，具體的變更可以參數 PR https://github.com/dotnet/efcore/pull/21862

Events

之前寫過兩篇關于 EF Core 做自動審計的文章

第一次的實現需要顯式繼承一個 AuditDbContext ，在有些需要沒辦法修改 DbContext 或者原有 DbContext 已經有繼承某一個類，就沒有辦法用了，可以參考?EF Core 數據變更自動審計設計

后面結合 AOP 改進了一版，通過一個審計切面邏輯完成自動審計，但是需要引入 AOP 組件支持，對于不想引入額外組件的項目來說也并非特別友好，可以參考?打造更好用的 EF 自動審計

在這個 PR 合并之后，我們可以通過 SavingChanges 事件獲取保存之前 DbContext 的狀態，通過 SavedChanges 事件來獲取保存成功后的 DbContext 信息，SaveChangesFailed 事件獲取保存失敗信息

事件定義如下：

///?<summary> ///?????An?event?fired?at?the?beginning?of?a?call?to?<see?cref="M:SaveChanges"/>?or?<see?cref="M:SaveChangesAsync"/> ///?</summary> public?event?EventHandler<SavingChangesEventArgs>?SavingChanges;///?<summary> ///?????An?event?fired?at?the?end?of?a?call?to?<see?cref="M:SaveChanges"/>?or?<see?cref="M:SaveChangesAsync"/> ///?</summary> public?event?EventHandler<SavedChangesEventArgs>?SavedChanges;///?<summary> ///?????An?event?fired?if?a?call?to?<see?cref="M:SaveChanges"/>?or?<see?cref="M:SaveChangesAsync"/>?fails?with?an?exception. ///?</summary> public?event?EventHandler<SaveChangesFailedEventArgs>?SaveChangesFailed;

事件參數定義如下：

///?<summary> ///?????Base?event?arguments?for?the?<see?cref="M:DbContext.SaveChanges"?/>?and?<see?cref="M:DbContext.SaveChangesAsync"?/>?events. ///?</summary> public?abstract?class?SaveChangesEventArgs?:?EventArgs {///?<summary>///?????Creates?a?base?event?arguments?instance?for?<see?cref="M:DbContext.SaveChanges"?/>///?????or?<see?cref="M:DbContext.SaveChangesAsync"?/>?events.///?</summary>///?<param?name="acceptAllChangesOnSuccess">?The?value?passed?to?SaveChanges.?</param>protected?SaveChangesEventArgs(bool?acceptAllChangesOnSuccess){AcceptAllChangesOnSuccess?=?acceptAllChangesOnSuccess;}///?<summary>///?????The?value?passed?to?<see?cref="M:DbContext.SaveChanges"?/>?or?<see?cref="M:DbContext.SaveChangesAsync"?/>.///?</summary>public?virtual?bool?AcceptAllChangesOnSuccess?{?get;?} }///?<summary> ///?????Event?arguments?for?the?<see?cref="DbContext.SavingChanges"?/>?event. ///?</summary> public?class?SavingChangesEventArgs?:?SaveChangesEventArgs {///?<summary>///?????Creates?event?arguments?for?the?<see?cref="M:DbContext.SavingChanges"?/>?event.///?</summary>///?<param?name="acceptAllChangesOnSuccess">?The?value?passed?to?SaveChanges.?</param>public?SavingChangesEventArgs(bool?acceptAllChangesOnSuccess):?base(acceptAllChangesOnSuccess){} }///?<summary> ///?????Event?arguments?for?the?<see?cref="DbContext.SavedChanges"?/>?event. ///?</summary> public?class?SavedChangesEventArgs?:?SaveChangesEventArgs {///?<summary>///?????Creates?a?new?<see?cref="SavedChangesEventArgs"?/>?instance?with?the?given?number?of?entities?saved.///?</summary>///?<param?name="acceptAllChangesOnSuccess">?The?value?passed?to?SaveChanges.?</param>///?<param?name="entitiesSavedCount">?The?number?of?entities?saved.?</param>public?SavedChangesEventArgs(bool?acceptAllChangesOnSuccess,?int?entitiesSavedCount)?:?base(acceptAllChangesOnSuccess){EntitiesSavedCount?=?entitiesSavedCount;}///?<summary>///?????The?number?of?entities?saved.///?</summary>public?virtual?int?EntitiesSavedCount?{?get;?} }///?<summary> ///?????Event?arguments?for?the?<see?cref="DbContext.SaveChangesFailed"?/>?event. ///?</summary> public?class?SaveChangesFailedEventArgs?:?SaveChangesEventArgs {///?<summary>///?Creates?a?new?<see?cref="SaveChangesFailedEventArgs"/>?instance?with?the?exception?that?was?thrown.///?</summary>///?<param?name="acceptAllChangesOnSuccess">?The?value?passed?to?SaveChanges.?</param>///?<param?name="exception">?The?exception?thrown.?</param>public?SaveChangesFailedEventArgs(bool?acceptAllChangesOnSuccess,?[NotNull]?Exception?exception):?base(acceptAllChangesOnSuccess){Exception?=?exception;}///?<summary>///?The?exception?thrown?during<see?cref="M:DbContext.SaveChanges"/>?or?<see?cref="M:DbContext.SaveChangesAsync"/>.///?</summary>public?virtual?Exception?Exception?{?get;?} }

More

除了上面的審計，你也可以使用通過這些事件，實現保存之前的自動更新數據庫字段的值，比如 Add 或 Update 操作數據時自動設置更新時間等信息

本文提到的特性還未正式發布，預計會在 .net5 下一個預覽版中發布，如果想現在要嘗試，請使用 efcore 的 daily build 的包，可以參考 https://github.com/dotnet/aspnetcore/blob/master/docs/DailyBuilds.md

Reference

• https://github.com/dotnet/efcore/issues/15910

• https://github.com/dotnet/efcore/pull/21862

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