Question

我想查询3个表并抓取所有表中的最近活动，由CreatedDate时间戳确定。每个表都由我的域模型中的实体表示，我使用实体框架代码优先（无数据迁移）来映射我的域。

我知道SQL中的查询应该是什么样的，但我不知道如何在LinqToEntities或EntitySql中创建它。您能否告诉我如何在Entity Framework中执行此操作，即使使用Entity Framework查询方法执行此查询也是合适的？

提前感谢您的帮助。

这是我的实体（主键在基类上）：

public class Group : EntityThatBelongsToApartmentComplex<int>
{
    public string GroupName { get; set; }
    public string GroupDescription { get; set; }

    [Required]
    public DateTimeOffset CreatedDate { get; protected set; }

    public int CreatedById { get; set; }
    public virtual UserProfile CreatedBy { get; set; }    
}


public class Activity : EntityThatBelongsToApartmentComplex<int>
{
    [StringLength(150)]
    public string Name { get; set; }

    [StringLength(150)]
    public string Description { get; set; }

    public int CreatedById { get; set; }
    public virtual UserProfile CreatedBy { get; set; }

    [Required]
    public DateTimeOffset CreatedDate { get; protected set; }       
}


public class Comment : EntityBase<int>
{
    [StringLength(200)]
    public string Text { get; set; }

    public int CreatedById { get; set; }
    public virtual UserProfile CreatedBy { get; set; }

    [Required]
    public DateTimeOffset CreatedDate { get; protected set; }
}

这是我对SQL中查询应该是什么样子的感觉：

WITH NewsFeed AS (
SELECT 
    g.Id AS ItemId
    ,'Group' AS ItemType
    ,g.GroupName AS HeaderText
    ,g.CreatedDate
    ,g.CreatedById AS CreatorId
    ,u.UserName AS CreatorName
FROM Groups g
    INNER JOIN UserProfiles u on g.CreatedById = u.Id

UNION 

SELECT 
    a.Id AS ItemId
    ,'Activity' AS ItemType
    ,a.Name AS HeaderText
    ,a.CreatedDate
    ,a.CreatedById AS CreatorId
    ,u.UserName
FROM Activities a
    INNER JOIN UserProfiles u on a.CreatedById = u.Id

UNION 

SELECT 
    c.Id AS ItemId
    ,'Comment' AS ItemType
    ,c.Text AS HeaderText
    ,c.CreatedDate
    ,c.CreatedById AS CreatorId
    ,u.UserName
FROM Comments c
    INNER JOIN UserProfiles u on c.CreatedById = u.Id
) 
SELECT TOP 10 *
    FROM NewsFeed
    ORDER BY CreatedDate

Answer 1

您需要使用投影。只需将每个查询的结果投影到具有相同参数的匿名（或非匿名）对象（名称和类型必须匹配）。然后你可以做这样的事情：

var query =
    context.SetOne.Select(x => new { Key = x.ID })
        .Union(context.SetTwo.Select(x => new { Key = x.AnotherKey }))
        .Union(context.SetThree.Select(x => new { Key = 5 }));

使用实体框架查询多个表的联合结果

1 个答案: