Linq 查询重写

Question

这真的难倒我了...

我有两个问题..

这个不工作，有错误， "LINQ to Entities does not recognize the method GetAllCustomers()' method, and this method cannot be translated into a store expression."

results = theDocuments.Select(x => new DocumentModel()
                {
                    document_id = x.document_id,
                    document_type = x.document_type,
                    franchisee_id = x.franchisee_id,
                    customer_id = x.customer_id,
                    address = x.address,
                    area_id = x.area_id,
                    ***HERE***customer_name = outletService.GetAllCustomers().Where(xx => xx.id == x.customer_id).First().name
                }).OrderBy(x => x.document_id);

现在像这样重写它：

results = from p in theDocuments
                          join cust in outletService.GetAllCustomers() on p.customer_id equals cust.id
                          select new DocumentModel()
                          {
                              customer_name = cust.name,
                              document_id = p.document_id,
                              document_type = p.document_type,
                              franchisee_id = p.franchisee_id,
                              customer_id = p.customer_id,
                              address = p.address
                          };

我知道这不能转换成相关的 SQL，但是，我不确定第二个查询在执行过程中做了哪些不同的工作，它是否执行了 GetAllCustomers( ) 在做其他事情之前？它在内部的工作方式有何不同？

如何重写第一个查询以使其正确执行？

谢谢，詹姆斯.

**这就是我最终得到的结果**

 results = theDocuments.Join(
                    outletService.GetAllCustomers(), docs => docs.customer_id, customers => customers.id, (doc, cust) => new DocumentModel()
                    {
                        document_id = doc.document_id,
                        document_type = doc.document_type,
                        franchisee_id = doc.franchisee_id,
                        customer_id = doc.customer_id,
                        address = doc.address,
                        area_id = doc.area_id,
                        customer_name = cust.name
                    });

Answer 1

第一个尝试将您的方法转换为 SQL 方法，第二个尝试在查询中创建连接。在我看来，正确的方法是使用 join :)

Answer 2

我是个问题。我找到了解决办法。这可能对你有帮助。

            dynamic user = new
            {
                Name = "",
                Surname = ""
            };

            dynamic userModel = new
            {
                Name = "",
                Surname = "",
                FullName = ""
            };

            var query = db.User.AsNoTracking();
            query = query.Select(x => new userModel
            {
                Name = x.Name,
                Surname = x.SurName,
                FullName = $"{x.Name}{x.SurName}",
            }).ToList();

如果您尝试执行此查询。你会崩溃的。 Linq 不支持

FullName = $"{x.Name}{x.SurName}"

您必须将此行更改为

FullName = x.Name + " " + x.SurName

Linq 查询重写

Linq query rewriting

c#

linq

linq-to-entities

iqueryable