Question

我的代码如下面的服务器端：

public CUSTOMER GetCustomerByNumber(string customerNumber){
            var customerInfo = (from c in db.CUSTOMER
                                where c.CUSTOMERNUMBER == customerNumber
                                select new CUSTOMER()
                                {
                                    Id = c.Id,
                                    FirstName = c.FirstName,
                                    LastName = c.LastName
                                }).SingleOrDefault();

            return customerInfo;
}

但是当我运行项目时，会显示以下错误：

无法在LINQ中构造实体或复杂类型“CUSTOMER” 到实体查询。

Answer 1

假设Customer是映射实体，则无法在Entity Framework中对Customer类进行预测。相反，你可以试试这个：

public CUSTOMER GetCustomerByNumber(string customerNumber){
        var customerInfo = (from c in db.T_CLUB_CUSTOMER
                            where c.C_CUSTOMER_NUMBER == customerNumber
                            select new 
                            {
                                Id = c.Id,
                                D_DEFINE = c.D_DEFINE,
                                B_IS_REAL = c.B_IS_REAL,
                                C_NATIONAL_CODE = c.C_NATIONAL_CODE
                            }).SingleOrDefault();

        return new Customer() { Id = customerInfo.Id };
}

此查询使用匿名类型进行投影。之后，您可以将匿名类型映射到Customer类型的实例。

或者，您可以使用不属于DbContext的类来进行投影（使用所谓的DTO）：

public CUSTOMERDTO GetCustomerByNumber(string customerNumber){
        var customerInfo = (from c in db.T_CLUB_CUSTOMER
                            where c.C_CUSTOMER_NUMBER == customerNumber
                            select new CUSTOMERDTO
                            {
                                Id = c.Id,
                                D_DEFINE = c.D_DEFINE,
                                B_IS_REAL = c.B_IS_REAL,
                                C_NATIONAL_CODE = c.C_NATIONAL_CODE
                            }).SingleOrDefault();

        return customerInfo;
}

注意这里的类是如何不同的（假设CUSTOMERDTO未在Entity Framework运行时中声明。

Answer 2

不CUSTOMER()你必须写Customer

public CUSTOMER GetCustomerByNumber(string customerNumber){
        var customerInfo = (from c in db.CUSTOMER
                            where c.CUSTOMERNUMBER == customerNumber
                            select new CUSTOMER // HERE
                            {
                                Id = c.Id,
                                FirstName = c.FirstName,
                                LastName = c.LastName
                            }).SingleOrDefault();

        return customerInfo;

但已经结果是客户你可以像这样写

var customerInfo = db.CUSTOMER.Where(c =>  c.CUSTOMERNUMBER == customerNumber).SingleOrDefault();

无法在LINQ to Entities查询

2 个答案: