Question

我的查询在下面给出。如果id = 0我也不希望在我的where子句中，如果title为空，那么我需要从where子句中删除它。是否有任何方法可以做到这一点。我是EF的新手我尝试了很多，但仍然没有运气。

public dynamic GetData(int id,string title){

    var entryPoint = (from ep in dbContext.tbl_EntryPoint
                     join e in dbContext.tbl_Entry on ep.EID equals e.EID
                     join t in dbContext.tbl_Title on e.TID equals t.TID
                     where e.OwnerID == id || t.title==title
                     select new {
                         UID = e.OwnerID,
                         TID = e.TID,
                         Title = t.Title,
                         EID = e.EID
                     }).Take(10);
}

Answer 1

有几个级别可以做到这一点。您可以使用where这样的where ((e.OwnerID == id) || (id == 0))子句将其嵌入到生成的SQL中，或者您可以完全采用另一种方式，并为不同的where子句分别创建整个LINQ表达式的四个副本变种。我个人推荐一种中途方法：使用单独的代码分支根据过滤器构建不同的IQueryable值，而不重复公共部分：

public dynamic GetData(int id, string title)
{
    var baseQuery =
        from ep in dbContext.tbl_EntryPoint
            join e in dbContext.tbl_Entry on ep.EID equals e.EID
            join t in dbContext.tbl_Title on e.TID equals t.TID
        select new { e, t };

    var filtered = baseQuery; // Implicitly type filtered to match the anonymous type in baseQuery

    if (id > 0)
    {
        if (!string.IsNullOrWhiteSpace(title))
            filtered = baseQuery.Where(ep => (ep.e.OwnerID == id) || (ep.t.title == title));
        else
            filtered = baseQuery.Where(ep => ep.e.OwnerID == id);
    }
    else
    {
        if (!string.IsNullOrWhiteSpace(title))
            filtered = baseQuery.Where(ep => ep.t.title == title);
        else
            filtered = baseQuery;
    }

    var entryPoint = filtered.Select(ep =>
        new
        {
            UID = ep.e.OwnerID,
            TID = ep.e.TID,
            Title = ep.t.Title,
            EID = e.EID
        }).Take(10);

    ...
}

实体框架足够聪明，知道在baseQuery中构建的匿名类型中，ep.e引用tbl_Entry连接表，而ep.t引用{ {1}}加入了表格。以下是上述代码生成的SQL示例：

tbl_Title

（这是使用非零SELECT [Limit1].[EID] AS [EID], [Limit1].[OwnerID] AS [OwnerID], [Limit1].[TID] AS [TID], [Limit1].[Title] AS [Title], [Limit1].[EID1] AS [EID1] FROM ( SELECT TOP (10) [Extent1].[EID] AS [EID], [Extent2].[EID] AS [EID1], [Extent2].[OwnerID] AS [OwnerID], [Extent2].[TID] AS [TID], [Extent3].[Title] AS [Title] FROM [dbo].[tbl_EntryPoint] AS [Extent1] INNER JOIN [dbo].[tbl_Entry] AS [Extent2] ON [Extent1].[EID] = [Extent2].[EID] INNER JOIN [dbo].[tbl_Title] AS [Extent3] ON [Extent2].[TID] = [Extent3].[TID] WHERE [Extent2].[OwnerID] = @p__linq__0 OR [Extent3].[Title] = @p__linq__1 ) AS [Limit1]和非空id生成的，因此在第一个title案例中失败，调用if用于测试.Where和id的表达式。）

如果在EF6中过滤器为空，如何删除where条件

1 个答案: