如何选择刚刚从EF表中的某些字段 [英] How to select just some fields from a table in EF

问题描述

我有一个数据库9列的表，我希望能够加载只有它的某些领域，如果我需要。

I have a table with 9 columns in database and I want to be able to load only some fields of it if I need.

我怎样才能做到这一点与实体框架4好吗？

How can I do this with Entity Framework 4 please?

例如。我的表有以下字段：

e.g. My table has these fields:

ID, FirstName, LastName, FotherName, BirthDate, Mobile, Email

和我希望能够获取只是这些列：

and I want to be able to fetch just these columns:

ID, FirstName, LastName

我的项目是一个 ASP.NET MVC 3 应用程序，其中的SQLServer 2008年防爆preSS 和 EF 4.1 。

推荐答案

假设你有这种模式的表格：

Assume you have a table with this model:

public class User{
    public int ID {get; set;}
    public string NickName {get; set;}
    public string FirstName {get; set;}
    public string LastName {get; set;}
    public string FotherName {get; set;}
    public DateTime BirthDate {get; set;}
    public string Mobile {get; set;}
    public string Email {get; set;}
    public string Password {get; set;}
}

现在，你要取只是 ID ，姓，姓和 FotherName 。你可以做到这一点在2路;第一种方式是获取它们作为一个匿名对象，看看：

Now, you want fetch just ID, FirstName, LastName, and FotherName. You can do it in 2 way; The first way is fetch them as an anonymous object, look:

var user = entityContext.Users.Where(u => u.ID == id)
    .Select(u => new {
        ID = u.ID,
        FirstName = u.FirstName,
        LastName = u.LastName,
        FotherName = u.FotherName
    }).Single();

现在，您的返回值类型是匿名，你可以使用它，例如：

Now, your return-value-type is anonymous, you can work with it such as:

var i = user.ID;
// or
var s = user.FirstName;

在另一种方式（例如，当您想要的通过的对象为型号到查看），你可以定义一个新的类（即 UserViewModel ），当您选择的对象，选择它作为一个 UserViewModel 。看：

In another way (for example when you want to pass the object as an Model to a View), you can define a new class, (i.e. UserViewModel), and when you select the object, select it as a UserViewModel. look:

public class UserViewModel{
    public int ID {get; set;}
    public string NickName {get; set;}
    public string FirstName {get; set;}
    public string LastName {get; set;}
    public string FotherName {get; set;}
}

和查询，借此：

var user = entityContext.Users.Where(u => u.ID == id)
    .Select(u => new UserViewModel {
        ID = u.ID,
        FirstName = u.FirstName,
        LastName = u.LastName,
        FotherName = u.FotherName
    }).Single();

看刚 ONE 的区别是它们之间，在labda前pression，而不是 U =＆GT;新{}
我们使用 U =＆GT;新UserViewModel {} 。祝你好运。

Look that just ONE difference is between them, in labda expression, instead of u => new {} we are using u => new UserViewModel{}. Good luck.

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