Linq outer join

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

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. 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.

The same results can be achieved using GroupJoin method, as follows:. Name equals s.

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. DepId into empDept from ed in empDept.

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.

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:. What would that operation look like in code?

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An excluding join returns non-matching data. Ethical Hacking. Interview Questions. Cyber Security. Using the "join" keyword we can do an inner join using a LINQ query. The second join clause correlates the anonymous types returned by the first join with Teacher objects based on that teacher's ID matching the department head ID. Let us see how we can do this. The following example is similar to the previous example except that instead of creating anonymous types, the result selector function creates XML elements that represent the joined objects. Now, we are getting NA in the address if the corresponding address is unavailable for an employee. The first example in this article shows you how to perform a group join. Recommended Free Ebook. 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. In this case, the un-matching data will take the default values.

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This is where joins come in handy. Company Questions. WriteLine item. DepId into empDept from ed in empDept. By using the site you accept the cookie policy. Jignesh Trivedi Nov 15, Data Science. Then we project the result using an anonymous type. The default value for a reference type is null ; therefore, the example checks for a null reference before accessing each element of each Student collection. The second example shows you how to use a group join to create XML elements. We can see that there are both matching and non-matching data. This allows you to select all of the items from the first sequence, which appears on the left of the statement, even if they have no matching values in the second.