实体框架核心和 Cosmos DB。使用 LINQ 表达式读取实体

Question

在我们的解决方案中，我们使用包 Microsoft.EntityFrameworkCore.Cosmos 3.1.1 对 Azure 中的 cosmos 数据库和容器进行操作。我们有一个相当简单的对象结构。一个对象包含其他对象的列表。

public class ExampleEntity : Entity
{
    public string TestProperty { get; set; }
    public IEnumerable<SubEntity> SubEntities { get; set; }

    protected override IEnumerable<object> GetEqualityComponents()
    {
            yield return TestProperty;
    }
}

public class SubEntity : Entity
{
    public bool IsActive { get; set; }

    protected override IEnumerable<object> GetEqualityComponents()
    {
        yield return IsActive;
    }
}

我们已经为 EntityFramework 配置了DbContext，如下所示：

builder.Entity<ExampleEntity>().ToContainer(nameof(ExampleEntity));
builder.Entity<ExampleEntity>().HasKey(p => p.id);
builder.Entity<ExampleEntity>().OwnsMany(p => p.SubEntities);

cosmos中的json结构是这样的：

{
    "id": "51099fa9-5d71-4181-93b1-2c8cc0482a95",
    "CreatedAt": "2020-02-14T08:11:06.701659Z",
    "Discriminator": "ExampleEntity",
    "TestProperty": "Property1",
    "UpdatedAt": "0001-01-01T00:00:00",
    "SubEntities": [
        {
            "id": "9a120613-c42a-4399-a660-e6228cfce0ad",
            "CreatedAt": "2020-02-14T08:11:06.70457Z",
            "ExampleEntityid": "51099fa9-5d71-4181-93b1-2c8cc0482a95",
            "IsActive": false,
            "UpdatedAt": "0001-01-01T00:00:00"
        },
        {
            "id": "21b86b53-2d6a-4b31-a60b-8d31cfd04734",
            "CreatedAt": "2020-02-14T08:11:06.705145Z",
            "ExampleEntityid": "51099fa9-5d71-4181-93b1-2c8cc0482a95",
            "IsActive": true,
            "UpdatedAt": "0001-01-01T00:00:00"
        }
    ],
    "_rid": "R343APAECLsBAAAAAAAAAA==",
    "_self": "dbs/R343AA==/colls/R343APAECLs=/docs/R343APAECLsBAAAAAAAAAA==/",
    "_etag": "\"06001f30-0000-0d00-0000-5e46561b0000\"",
    "_attachments": "attachments/",
    "_ts": 1581667867
}

现在，我们要搜索ExampleEntities，其中SubEntities 的布尔值IsActive 设置为true。这就是我们的问题开始的地方。

我们有一个通用存储库，其中 Read 方法如下所示：

/// <summary>
/// Get an entity from the database
/// </summary>
/// <param name="predicate">A predicate to decide which entity to get</param>
/// <param name="children">Child entities to included in the DbSet</param>
/// <returns>All entities that matches the predicate</returns>
public async Task<IEnumerable<TEntity>> ReadAsync(Expression<Func<TEntity, bool>> predicate, params Expression<Func<TEntity, object>>[] children)
{
    var dbSet = _dbContext.Set<TEntity>();
    children.ToList().ForEach(p => dbSet.Include(p));

    var entities = dbSet.Where(predicate);
    return await entities.ToListAsync();
}

在 IntegrationTest 中使用如下代码：

[Test]
public async Task EntityFramework_Should_Return_Object_Based_On_Property_In_SubEntity()
{
    var uow = Container.Resolve<IUnitOfWork<ExampleEntity>>();
    var entity1 = new ExampleEntity
    {
        TestProperty = "Property1",
        SubEntities = new List<SubEntity>
        {
            new SubEntity
            {
                IsActive = false
            },
            new SubEntity
            {
                IsActive = true
            }
        }
    };

    await uow.Repository.CreateAsync(entity1);
    await uow.CommitAsync();

    var readEntity = uow.Repository.ReadAsync(p => p.SubEntities.Any(p => p.IsActive), p => p.SubEntities);
    readEntity.Should().NotBeNull();
}

问题发生在我使用上面存储库中的 Read 方法的这一行：

var readEntity = uow.Repository.ReadAsync(p => p.SubEntities.Any(p => p.IsActive), p => p.SubEntities);

导致以下异常：

System.InvalidOperationException: The LINQ expression 'DbSet<ExampleEntity>
    .Where(e => EF.Property<IEnumerable<SubEntity>>(e, "SubEntities")
        .AsQueryable()
        .Any(o => o.IsActive))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync().

我觉得很奇怪，Entity Framework Cosmos 不支持这样的简单查询。显然我可以做一个AsEnumerable()，但是我会从数据库下载所有数据并在客户端而不是数据库端进行过滤，当数据库包含100'000条记录时，这将对性能产生巨大影响。 .

如何重写我的存储库以在数据库端进行此类过滤？ Entity Framework Cosmos 有可能吗？

Answer 1

根据current limitations Include 和join 尚不支持。