Linq outer join

Posted by Kamil Pakula Mar 6, 0. Want to build great APIs?

The syntax of using the LINQ Left Outer Join to get all the elements from the collection and matching the element from the right collection. From the above syntax, we used into and DefaultfEmpty methods to implement the left outer join to get the elements from the " objEmp1 ", " objDept1 " collections. From the above example, we are getting the elements from " objEmp1 ", " objDept1 " collections by using left outer join in LINQ and here we specified the condition to check if there is a department for the employee or not. In case if the department not mapped, it will take " No Department " from the condition. LINQ Tutorial.

Linq outer join

This article explains various types of joins in LINQ query. Introduction SQL joins are used to get data from two or more tables, based on the logical relationships between the tables. There are mainly the following four types of joins available with SQL Server:. LINQ is a full-featured query language. I have two tables: EmployeeMaster and DepartmentMaster. The relation between these two tables and dummy data for the tables are as shown below. An inner join returns only those records that exist in the tables. Using the "join" keyword we can do an inner join using a LINQ query. A Left Outer join returns all records from the left table and the matching record from the right table. If there are no matching records in the right table then it returns null.

In the below example, we are projecting the result to an anonymous type. DepId into empDept from ed in empDept. Generic; using System.

Please read the following three articles before proceeding to this article, as they all are required to understand the Left Outer Join. The Left Join or Left Outer Join is a Join in which each data from the first data source will be returned irrespective of whether it has any correlated data present in the second data source. In this case, the un-matching data will take a null value. For a better understanding, please look at the following diagram, which shows the graphical representation of the Left Outer Join. So, in simple words, we can say that the Left Outer Join will return all the matching data from both the data sources and all the non-matching data from the left data source. In such cases, the non-matching data will take null values for the second data source. In LINQ, you can perform a left join operation between two collections or tables in a database using the join keyword followed by the into keyword to create a temporary grouping of results.

Please read the following three articles before proceeding to this article, as they all are required to understand the Left Outer Join. The Left Join or Left Outer Join is a Join in which each data from the first data source will be returned irrespective of whether it has any correlated data present in the second data source. In this case, the un-matching data will take a null value. For a better understanding, please look at the following diagram, which shows the graphical representation of the Left Outer Join. So, in simple words, we can say that the Left Outer Join will return all the matching data from both the data sources and all the non-matching data from the left data source.

Linq outer join

Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. A join of two data sources is the association of objects in one data source with objects that share a common attribute in another data source. Joining is an important operation in queries that target data sources whose relationships to each other can't be followed directly. In object-oriented programming, joining could mean a correlation between objects that isn't modeled, such as the backwards direction of a one-way relationship. An example of a one-way relationship is a Student class that has a property of type Department that represents the major, but the Department class doesn't have a property that is a collection of Student objects. If you have a list of Department objects and you want to find all the students in each department, you could use a join operation to find them. These methods perform equijoins, or joins that match two data sources based on equality of their keys. For comparison, Transact-SQL supports join operators other than equals , for example the less than operator.

Masculine birthday wishes

Here, we specify what it means for two SongWithAuthor objects to be equal. DepId into empDept from ed in empDept. Next we add a second from clause that gets data from the temporary variable with a call to DefaultIfEmpty. Generally, in SQL, a group join can be done using a "Group by" clause. It returns a sequence of anonymous types that contain the Student object and Department object. Generic; using System. In the main part the results are identical to the inner join. Instead of correlating elements based on just one property, you can use a composite key to compare elements based on multiple properties. The only difference is that we swap the data sources. In both cases, the non-matching data takes the null value or any default value that we provide. We have also created one method, i. In the example below, we display the value NA if the corresponding address is unavailable.

It returns a new collection that contains elements from both the collections which satisfies specified expression.

With the above changes in place, run the application, and you will also get the same output as the previous example, as shown in the below image. These are the properties used for matching. There is query syntax and method syntax. The list of Department objects is group-joined to the list of Student objects based on the Department. DepartmentId into dept from department in dept. In this example, the list of Department objects is inner-joined to the list of Student objects based on a Department object's ID that matches the student's DepartmentID. A right outer join is not possible with LINQ. The join operation compares these composite keys for equality and returns pairs of objects from each list where both the first name and the family name match. The category includes a name and the name of the major category that it belongs to. So, first, create a class file with the name Employee. The group join produces an inner join. For a better understanding, please look at the following diagram, which shows the graphical representation of the Left Outer Join.