EF 10 LeftJoin & RightJoin 的支持

郑子铭

发布于 2025-04-27 13:26:23

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文章被收录于专栏：DotNet NB && CloudNativeDotNet NB && CloudNative

EF 10 LeftJoin & RightJoin 的支持

Intro

我们前面介绍 Linq LeftJoin/RightJoin 的时候提到过 EF Core 也会支持 LeftJoin/RightJoin，EF Core 在 preview 1 的时候支持了 LeftJoin 在 preview 2 中支持了 RightJoin，现在 preview 2 已经发布我们一起来看下吧

Sample

测试示例如下：

public static async Task EFLeftRightJoinSample()
{
    var services = new ServiceCollection();
    services.AddSqlite<TestDbContext>("Data Source=test.db", optionsAction: options =>
    {
        options.LogTo(Console.WriteLine);
    });
    awaitusingvar serviceProvider = services.BuildServiceProvider();

    usingvar scope = serviceProvider.CreateScope();
    var dbContext = scope.ServiceProvider.GetRequiredService<TestDbContext>();
    await dbContext.Database.EnsureDeletedAsync();
    await dbContext.Database.EnsureCreatedAsync();

    dbContext.Jobs.Add(new Job() { Id = 1, Name = "test" });
    dbContext.Employees.Add(new Employee() { Id = 1, JobId = 1, Name = "Alice" });
    dbContext.Employees.Add(new Employee() { Id = 2, JobId = 2, Name = "Jane" });
    await dbContext.SaveChangesAsync();

    var result = await dbContext.Employees.AsNoTracking()
        // ReSharper disable once EntityFramework.UnsupportedServerSideFunctionCall
        .LeftJoin(dbContext.Jobs.AsNoTracking(), e => e.JobId, j => j.Id, (e, j) => new
        {
            e.Id,
            e.Name,
            e.JobId,
            JobName =  j == null ? "Unknown" : j.Name
        })
        .ToArrayAsync();
    foreach (var item in result)
    {
        Console.WriteLine(JsonSerializer.Serialize(item));
    }

    result = await dbContext.Jobs.AsNoTracking()
        // ReSharper disable once EntityFramework.UnsupportedServerSideFunctionCall
        .RightJoin(dbContext.Employees.AsNoTracking(), j => j.Id, e => e.JobId, (j, e) => new
        {
            e.Id,
            e.Name,
            e.JobId,
            JobName =  j == null ? "Unknown" : j.Name
        })
        .ToArrayAsync();
    foreach (var item in result)
    {
        Console.WriteLine(JsonSerializer.Serialize(item));
    }
}

为了方便看测试结果我们将 Log 输出到 Console 里方便打印实际数据库的查询是否符合预期

LeftJoin

RightJoin

从上面执行的 SQL 可以看得出来我们的 LeftJoin & RightJoin 被正确翻译成了 SQL

大家留意代码的话会发现有一行注释

// ReSharper disable once EntityFramework.UnsupportedServerSideFunctionCall

这行注释是给 Resharper 和 Rider 的，不加的话目前会有一个 warning，示例如下：

在之前的版本里不能转成 SQL 但从 EF Core 10 开始就可以了，ReSharper 后续应该会有所改进避免对 LeftJoin/RightJoin 产生 warning 吧

References

https://github.com/dotnet/efcore/issues/35379
https://github.com/dotnet/efcore/issues/12793
https://github.com/dotnet/efcore/pull/35451
https://github.com/dotnet/efcore/issues/35367
https://github.com/dotnet/efcore/pull/35462
https://github.com/WeihanLi/SamplesInPractice/blob/main/net10sample/Net10Samples/LinqSamples.cs#L74

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原始发表：2025-04-27，如有侵权请联系 cloudcommunity@tencent.com 删除

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