不能在LINQ到实体查询中构造asp.net mvC语言 class

Question

服务器端的代码如下:

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显示以下错误:

实体或复杂类型'CUSTOMER'不能在LINQ中构造to Entities查询

Answer 1

在实体框架中不可能对Customer类进行投影，假设Customer是一个映射实体。相反，您可以尝试这样做:

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 };
}

该查询使用匿名类型进行投影。然后，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的类来执行投影(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没有在实体框架运行时中声明)。

Answer 2

不是CUSTOMER()，必须写成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;

但是结果已经是Customer了，你可以这样写

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