组加入 EF Core 3.1

Question

我正在尝试组加入 EF core 3.1 问题呢returns

Processing of the LINQ expression 'DbSet failed. This may indicate either a bug or a limitation in EF Core

我的代码是这样的

 var employees = await (from enrollment in RepositoryContext.Enrollments
                join allowance in RepositoryContext.Allowances.Include(y=>y.AllowanceType) on enrollment.EmployeeId equals allowance.EmployeeId
                    into allowances

                select new
                {
                    enrollment,
                    allowances

                }
            ).AsNoTracking().ToListAsync();

allowances 是物品清单，运行像这样的查询是否有任何解决方法，因为我需要它以获得更好的性能。

Answer 1

在这里Query with GroupBy or GroupJoin throws exception is the now closed GitHub issue/discussion where I was trying to convince EF Core team to add GroupJoin translation. They refused to do that and opened the useless Query: Support GroupJoin when it is final query operator #19930我继续为这样的翻译而战。所以请去那里 comment/vote 提交完整的翻译请求。

您还会在那里找到解决方法 - 而不是不受支持的 GroupJoin 使用等效的受支持的相关子查询方法，例如替换

join allowance in RepositoryContext.Allowances.Include(y => y.AllowanceType)
    on enrollment.EmployeeId equals allowance.EmployeeId
into allowances

和

let allowances = RepositoryContext.Allowances.Include(y => y.AllowanceType)
    .Where(allowance => enrollment.EmployeeId == allowance.EmployeeId)

组加入 EF Core 3.1

Group join in EF Core 3.1

c#

entity-framework-core

linq-to-entities

asp.net-core-3.1

entity-framework-core-3.1