CODEWITHSUNDEEP
asp.net-mvclinq
Armita
Armita

Reputation: 33

class cannot be constructed in a LINQ to Entities query

My code is like below on the server side:

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;
}

but when I run the project the following error is shown:

The entity or complex type 'CUSTOMER' cannot be constructed in a LINQ to Entities query.

Upvotes: 2

Views: 62

Answers (2)

neer
neer

Reputation: 4082

Not CUSTOMER() You have to write 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;

But already result is Customer You can write like this

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

Upvotes: 0

hbulens
hbulens

Reputation: 1969

Projections on the Customer class is not possible in Entity Framework, assuming Customer is a mapped entity. Instead, you can try this:

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 };
}

This query uses an anonymous type to do the projection. Afterwards you can map the anonymous type to an instance of your Customer type.

Alternatively, you can use a class that is not part of your DbContext to do the projection (using so called DTOs):

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;
}

Notice how the class is different here (assuming CUSTOMERDTO is not declared in the Entity Framework runtime.

Upvotes: 2

Related Questions