ASP.NET/SQL-使用外键从多个表中检索数据

Question

I'm new to ASP.NET and SQL, and I'm trying to build a Web Forms project that will basically display data using grids.

I'm using Entity Framework along with a Data Transfer Object and a Data Access Layer for displaying/editing data.

My issue is that I'm not sure what is the best way of retrieving data using foreign keys.

Example:

Table 1 - Products

|(PK) Product ID | Product Name | Country ID(FK)

Table 2 - Countries

|(PK) Country ID | Country Name|

Final Result Should be:

Product ID | Product Name | Country Name|

What's the best way to accomplish that?

Thanks in advance

Answer 1

You can make LINQ query from this one. Better, you create one separate class and retrieve only data which you want.

SQL Query :

SELECT P.ProductID, P.ProductName, C.COuntryName FROM Products P
INNER JOIN ON Countries C ON C.CountryID = P.CountryID

Execute Query using EF :

context.Database.SqlQuery<ProductDTO>(query).ToList();

Answer 2

The best approach is use a projection to do that. Your code will be similar to the code below:

context.Products.Select(x=>new ProductDto
{
   ProductId=x.ProductId,
   ProductName=x.Name,
   CountryName=x.Country.Name
});

Using projections you will ensure that is retrieving only the necessary data from DB.

Hope this helps!