EF Core joining tables using Include and selecting specific columns

In the previous posts we saw on how to join tables using Include and how to select specific columns form a table. In this post we will try to combine both of them, we will join tables using Include and select specific columns from the joined tables.

We will join the Employee table with Department and Country tables, select specific columns from each of the table and populate the below Model class.

EF Core Joining tables with Include

In the previous pose we saw on how to join tables using the join keyword. Entity Framework core also provides an alternate way to join tables using the Include clause.  To use include for joining the tables we need to set the Primary Key, Foreign Key relation in the Database. 

In the sample we have an Employee table which has a Foreign Key DepartmentId referencing to the Department table. We will join these tables using Entity Framework Core.

Asp.Net EF Core Joining multiple tables

In the previous post we creates a custom model class EmployeeDetail, in this post we shall see on how to use Entity Framework Core to JOIN the Employee, Department and Country tables and populate data into the custom Model class EmployeeDetail.

We have 3 tables, the Employee table is the main table which has related data in the Department and Country tables, DepartmentId and CountryId are the Foreign Keys in the employee table.

LINQ to SQL – INNER JOIN

LINQ to SQL – INNER JOIN

Before writing a LINQ to SQL query, we first need to create a DataContext using the LINQ to SQL Classes template, to know more on how to create the DataContext refer to the post LINQ to SQL Sample

Once the DataContext is created we can query the Object model using LINQ queries, let us consider the Employee table which has the following structure.

In practical situations we will have to join more than one table to get the details for reporting.

An INNER JOIN is used to fetch the matching details from 2 or more tables.

Assume we have the following data in the Employee and Department Tables

Table: Employee

ID	NAME	Phone	Email	DepartmentID	Salery
1	Tom	123-123-1234	tom@abcsoftware.com	1	5000
2	Harry	123-123-1234	harry@abcsoftware.com	2	6000
3	Peter	111-222-3333	peter@abcsoftware.com	3	6500
4	John	111-222-3333	john@abcsoftware.com	3	7500
5	Charles	666-444-2222	charles@abcsoftware.com	NULL	6500

Table: Department

ID	NAME
1	Finance
2	Human Resources
3	IT
4	Sales
5	Marketing

The INNER JOIN SQL Query to join the 2 tables is as follows

SELECT     E.ID, E.Name, E.Phone, D.Name AS Department

FROM         Employee AS E INNER JOIN

                      Department AS D ON E.DepartmentID = D.ID

This query will fetch the following data

ID	NAME	Phone	Department
1	Tom	123-123-1234	Finance
2	Harry	123-123-1234	Human Resources
3	Peter	111-222-3333	IT
4	John	111-222-3333	IT

Now let us see how the same can be achieved using a LINQ query.

EmployeeClassesDataContext dbContext = new EmployeeClassesDataContext();

var emp = (from e in dbContext.Employees

                       join d in dbContext.Departments

                       on e.DepartmentID equals d.ID

                       select new { e.ID, e.Name, e.Phone, Department = (d.Name) });

Related Post

What is LINQ?
LINQ to SQL
LINQ To SQL Vs ADO.Net Entity Framework
LINQ to SQL Sample
LINQ to SQL Select Query with Specific columns
LINQ to SQL Select query with Filter (WHERE Clause)
LINQ to SQL Select Query with Alias Name
LINQ to SQL - Sub Queries
LINQ to SQL – Join 2 Tables
LINQ to SQL – Select DISTINCT Values
LINQ to SQL – Select with SORT (ORDER BY)
LINQ to SQL – Select with AGGREGATE (GROUP BY)
LINQ to SQL – INNER JOIN
LINQ to SQL – LEFT OUTER JOIN
LINQ to SQL – RIGHT OUTER JOIN
LINQ to SQL – INSERT
LINQ to SQL – UPDATE
LINQ to SQL – DELETE
LINQ to SQL – Using ExecuteCommand() to Execute SQL Statements