Why var in linq

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Remember me Forgot Password? Login Please Wait Sign in with Facebook. Don't have DotNetTricks account? Sign Up. We can achieve the same result without association properties as follows: from c in db. Customers where c. This is true only if you want a flat result set.

The examples in the preceding myth, for instance, translate to a left outer join in SQL, and require no DefaultIfEmpty operator. LINQ follows a lazy evaluation model, which means queries execute not when constructed , but when enumerated. This means you can build up a query in as many steps as you like, and it won't actually hit the server until you eventually start consuming the results.

For instance, the following query retrieves the names of all customers whose name starts with the letter 'A', and who have made at least two purchases. We build this query in three steps:. This strategy will result in stale data, because objects tracked by a DataContext instance are not refreshed simply by requerying.

Using a single static DataContext instance in the middle tier of a distributed application will cause further trouble, because DataContext instances are not thread-safe.

The correct approach is to instantiate fresh DataContext objects as required, keeping DataContext instances fairly short-lived. The same applies with Entity Framework. The expression: from c in db. Customers select c is a frivolous query! You can simply go: db. For instance, here's how to retrieve the names and IDs of all customers who have made no purchases: from c in db. Customers where! ID, c. This is a consequence of Myth 4. Declare the array with the var keyword in C We can use the var keyword to declare array data types where we don't have predefined datatypes as shown in the example below.

We see here how declaring an array with a var datatype does not bother us with the type of data of each element in the array. Just use a foreach loop with one var variable to find all the elements in the array. Use of var is useful when the type of a variable is unknown. Next Recommended Reading. Windows 10 Vs Windows Visual Studio Vs Visual Studio Understanding Matplotlib With Examples. Understanding Numpy With Examples.