EntityFrameWork Core 批量操作

在EF7.0的更新中，新增了批量更新和批量删除的功能：

批量删除：ExecuteDelete

对 DbSet 调用 ExecuteDelete 或 ExecuteDeleteAsync 会立即从数据库中删除该 DbSet 的所有实体。例如，删除所有 Tag 实体：

1	`await context.Tags.ExecuteDeleteAsync();`

使用 SQL Server 时，这将执行以下 SQL：

DELETE FROM [t]
FROM [Tags] AS [t]

查询可以包含筛选器：

await context.Tags.Where(t => t.Text.Contains(".NET")).ExecuteDeleteAsync();

这会执行以下 SQL：

DELETE FROM [t]
FROM [Tags] AS [t]
WHERE [t].[Text] LIKE N'%.NET%'

批量更新：ExecuteUpdate

await context.Blogs.ExecuteUpdateAsync(
    s => s.SetProperty(b => b.Name, b => b.Name + " *Featured!*"));

SetProperty 的第一个参数指定要更新的属性;在本例中，Blog.Name。第二个参数指定应如何计算新值；在本例中，通过获取现有值并追加 "*Featured!*"。生成的 SQL 为：

UPDATE [b]
SET [b].[Name] = [b].[Name] + N' *Featured!*'
FROM [Blogs] AS [b]

与 ExecuteDelete 一样，查询可用于筛选更新的实体。此外，可以使用多个调用 SetProperty 来更新目标实体上的多个属性。

await context.Posts
    .Where(p => p.PublishedOn.Year < 2022)
    .ExecuteUpdateAsync(s => s
        .SetProperty(b => b.Title, b => b.Title + " (" + b.PublishedOn.Year + ")")
        .SetProperty(b => b.Content, b => b.Content + " ( This content was published in " + b.PublishedOn.Year + ")"));

在这种情况下，生成的 SQL 稍微复杂一些：

UPDATE [p]
SET [p].[Content] = (([p].[Content] + N' ( This content was published in ') + COALESCE(CAST(DATEPART(year, [p].[PublishedOn]) AS nvarchar(max)), N'')) + N')',
    [p].[Title] = (([p].[Title] + N' (') + COALESCE(CAST(DATEPART(year, [p].[PublishedOn]) AS nvarchar(max)), N'')) + N')'
FROM [Posts] AS [p]
WHERE DATEPART(year, [p].[PublishedOn]) < 2022