Linq outer join

This article explains various types of joins in LINQ query. Introduction SQL joins are used to get data from two linq outer join more tables, based on the logical relationships between the tables. There are mainly the following four types of joins available with SQL Server:.

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. DeptId equals d.

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. In relational database terms, Join implements an inner join, a type of join in which only those objects that have a match in the other data set are returned. The GroupJoin method has no direct equivalent in relational database terms, but it implements a superset of inner joins and left outer joins. A left outer join is a join that returns each element of the first left data source, even if it has no correlated elements in the other data source. The following illustration shows a conceptual view of two sets and the elements within those sets that are included in either an inner join or a left outer join. Each Student has a grade level, a primary department, and a series of scores. A Teacher also has a City property that identifies the campus where the teacher holds classes. A Department has a name, and a reference to a Teacher who serves as the department head.

In the above example, linq outer join, query variable contains the query that creates a list where each element is an anonymous type that contains the department's name and a collection of students that study in that department.

Posted by Kamil Pakula Mar 6, 0. Want to build great APIs? Or become even better at it? Check our Ultimate ASP. NET technologies. Bonus materials Security book, Docker book, and other bonus files are included in the Premium package! We often use just a single data source.

It returns a new collection that contains elements from both the collections which satisfies specified expression. It is the same as inner join of SQL. As you can see in the first overload method takes five input parameters except the first 'this' parameter : 1 outer 2 inner 3 outerKeySelector 4 innerKeySelector 5 resultSelector. Let's take a simple example. The following example joins two string collection and return new collection that includes matching strings in both the collection. In the above example of join query, studentList is outer sequence because query starts from it. First parameter in Join method is used to specify the inner sequence which is standardList in the above example. Second and third parameter of Join method is used to specify a field whose value should be match using lambda expression in order to include element in the result.

Linq outer join

I think most C developers would agree that LINQ is an integral part of the experience of writing code with the language. LINQ provides a fluent, intuitive, and consistent way to query data sets. LINQ is available in two different flavors, the query syntax and the method syntax. When working with data, a common scenario is having two data sources that you want to combine based on some criteria. For instance, you might have a Books table and an Authors table in your database, with a one-to-many relationship between them—i. A join in LINQ is essentially the same: an operation where you can merge two collections according to some criteria you define. Examples always make things clearer. You can see where this is leading, right? In other words, a view like this:.

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Both of these operations can be written in terms of a grouped join. This class has 3 properties, i. 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. Text; using System. There are two ways to do a group join in LINQ. The following code demonstrates this equivalent query:. As you can see, even though Anurag and Pranaya do not have the corresponding address, they are still returned as part of the result set. Verbal Ability. DepartmentMasters join e in Context. We can use inner joins when we need to combine matching data coming from different sources. Finally, the result selector function creates an anonymous type for each match that consists of Department. Joining is an important operation in queries that target data sources whose relationships to each other can't be followed directly. Jignesh Trivedi Nov 15,

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.

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. Text; using System. Verbal Ability. Now, run the application, and you will get the following output. Computer Organization. Generic; using System. View all page feedback. In relational database terms, an inner join produces a result set in which each element of the first collection appears one time for every matching element in the second collection. If we were using query syntax, we would end up with the same result. We can visualize it as the difference between the full outer join and the inner join:.