Why Does My LINQ to Entities Query Throw 'The entity cannot be constructed in a LINQ to Entities query'?

Linq to Entities query error: "Can't construct entities in Linq to Entities query"

When using Entity Framework, be sure to check the abnormalities that may occur during the execution process. A common error is "Constructing entities in the Linq To Entities query", this error occurs when trying to projected the query result to the peripheral entities.

The reason for the error

In a given code fragment, query:

Try to project the query results on a new instance of the product entity. However, in the Linq to Entities query, the entity cannot be constructed or rebuilt, because the object of the object is managed by ORM.

from p in db.Products
where p.CategoryID == categoryID
select new Product { Name = p.Name };

Solution: Use anonymous type or DTO

In order to overcome this error and perform a customized option, you can use anonymous type or data transmission object (DTO). Anonymous type is a temporary naming type that can save a set of attributes, while DTO is a custom class that indicates a specific domain object. Create DTO

In this example, since you only need the name attribute, you can create DTO in the following way:

Modify the inquiry to be projected to DTO

With DTO, you can now modify the inquiry to projected it on the DTO:

public class ProductDTO
{
    public string Name { get; set; }
}

Through projection to DTO, you can successfully retrieve data and avoid "constructing entity in Linq to Entities inquiry" error.

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