Linq outer join

Posted by Kamil Pakula Mar 6, 0.

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.

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.

Table of contents Exit focus mode. Instead of projecting the result to linq outer join anonymous type, we can also project the result to a named type with LINQ Method Syntax. Support Code Maze on Patreon to get rid of ads and get the best discounts on our products!

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.

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:. What would that operation look like in code?

Linq outer join

Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. Microsoft makes no warranties, express or implied, with respect to the information provided here. Correlates the elements of two sequences based on matching keys.

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In case if the department not mapped, it will take " No Department " from the condition. 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. 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. A left outer join is a join in which each element of the first collection is returned, regardless of whether it has any correlated elements in the second collection. This class has two properties, i. It returns a sequence of anonymous types that contain the student's name, the department name, and the department leader's name. But sometimes we need data from more than one source, be it a database, a file, or a C collection, to mention just a few. That type is an anonymous type that consists of the student's name and the matching department name. To do that, we need a method that returns the inner join:. Because this operation is an inner join, only those objects from the first data source that have a match in the second data source are returned.

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.

Notify of. Coming soon: Throughout we will be phasing out GitHub Issues as the feedback mechanism for content and replacing it with a new feedback system. The right join will contain all the matching data and the remaining data from the authors list. The relation between these two tables and dummy data for the tables are as shown below. The following example demonstrates how to use the DefaultIfEmpty method on the results of a group join to perform a left outer join. Similarly, in a right outer join aka right join , all data from the second source is returned besides the matching data. To begin, let's look at an inner join of the stock items and category data, so that we can compare the syntax with that of a left outer join. We have already created a type called EmployeeResult. The other types include the full outer join , left excluding join , right excluding join, and full outer excluding join. Instead of correlating elements based on just one property, you can use a composite key to compare elements based on multiple properties. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.