# entityframework 部分欄位更新 與 部分欄位不更新
###### tags: `程式設計`

## 範例程式碼
先附上完整範例

public ActionResult Edit(Models.ModelClass postback)
{
    if (ModelState.IsValid) //判斷資料輸入是否正確
    {
        //部分欄位從後台更新
        postback.UpdateTime = DateTime.Now;

        //大多數欄位從post資料更新
        db.Entry(postback).State = EntityState.Modified;

        // 部分欄位不更新
        var excluded = new[] { "CreateTime","Other" };
        var entry = db.Entry(postback);
        entry.Property("CreateTime").IsModified = false;

        db.SaveChanges();

        return View();
}

## 部分欄位不更新 採用迴圈方式執行

var excluded = new[] { "Column1","Column2" };
var entry = db.Entry(postback);
foreach (var name in excluded)
{
    entry.Property(name).IsModified = false;
}
                

## .Add() 和 .Attach() 的差別
.Add() 不會立刻更新到資料庫，要等到執行 .SaveChanges() 的時候才會更新。
.Attach() 會立刻更新到資料庫。

## 參考資料
* Entity Framework - 為什麼修改的資料不用Attach
http://blog.sanc.idv.tw/2014/08/entity-framework-attach.html
* ASP.NET WEB API 2:安全的PATCH方法的三種實作
https://blog.kkbruce.net/2014/05/aspnet-webapi-2-security-PATCH-method-3-implement-ways.html#.YFlhkK8zZPY
* Entity Framework validation with partial updates
https://stackoverflow.com/questions/12871892/entity-framework-validation-with-partial-updates
* EntityFramework update partial model
https://stackoverflow.com/questions/9820540/entityframework-update-partial-model/9821029#9821029
* How to update not every fields of an object using Entity Framework and EntityState.Modified
https://stackoverflow.com/questions/10257360/how-to-update-not-every-fields-of-an-object-using-entity-framework-and-entitysta
* DbSetMigrationsExtensions.AddOrUpdate 方法
https://docs.microsoft.com/zh-tw/dotnet/api/system.data.entity.migrations.dbsetmigrationsextensions.addorupdate?view=entity-framework-6.2.0