在 Entity Framework Core 3.1 中使用投影时不会跟踪更改

Question

有预测（0 个变化）：

var changesBefore = Db.ChangeTracker.Entries<OrderLocationEntity>().ToList(); //before change - 0

var orderLocation = Db.OrderLocation.AsTracking().Select(ol => new OrderLocationEntity
{
    Id = ol.Id,
    Address = ol.Address,
    City = ol.City,
    Created = ol.Created,
    OrderId = ol.OrderId,
    Zip = ol.Zip
}).First();

orderLocation.Address = "address";

var changesAfter = Db.ChangeTracker.Entries<OrderLocationEntity>().ToList(); //after change - 0

没有投影（1 处更改）

var changesBefore = Db.ChangeTracker.Entries<OrderLocationEntity>().ToList(); //before change - 0

var orderLocation = Db.OrderLocation.AsTracking().First();

orderLocation.Address = "address";

var changesAfter = Db.ChangeTracker.Entries<OrderLocationEntity>().ToList(); //after change - 1

设置

Microsoft.EntityFrameworkCore 3.1.1

Microsoft.EntityFrameworkCore.sqlite 3.1.1

var options = new DbContextOptionsBuilder<OrderDatabaseContext>()
                .UseSqlite("DataSource=:memory:")
                .Options;

If the result set contains entity types coming out from LINQ composition, EF Core will track them.

来源

https://docs.microsoft.com/en-us/ef/core/querying/tracking

为什么在使用投影时未跟踪更改？

Answer 1

因为他们不跟踪他们。这在 3.1 中被禁用，其中项目自动添加 AsNoTracking。

许多许多无法真正解释并使 EfCore 3.1 成为无法与 Ef 6.4 竞争的产品的决定中的一个。

Answer 2

通知"entity types":

If the result set contains entity types coming out from LINQ composition, EF Core will track them.

来自相同的文档：

If the result set doesn't contain any entity types, then no tracking is done.

您的投影不包含实体类型，因此不会跟踪更改。

例如，如果您将引入属性来保留 OrderLocationEntity 个实例，则该实例将被上下文跟踪

var location = Db.OrderLocation.AsTracking()
    .Select(ol => new OrderLocationEntity
    {
        Id = ol.Id,
        Address = ol.Address,
        City = ol.City,
        Created = ol.Created,
        OrderId = ol.OrderId,
        Zip = ol.Zip,
        Location = ol // entity instance passed to the projected object
    })
    .First();

location.Location.Address = "New Address"; 

Db.ChangeTracker.Entries<OrderLocationEntity>().ToList(); //after change - 1

在 Entity Framework Core 3.1 中使用投影时不会跟踪更改

Changes are not tracked when using projections in Entity Framework Core 3.1

c#

entity-framework-core

.net-core

entity-framework-core-3.1