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This article is to share with you about how to achieve LINQ query statements, the editor feels very practical, so share with you to learn, I hope you can learn something after reading this article, say no more, follow the editor to have a look.

There are three steps to implementing a LINQ query statement. They are getting the data source (the necessary work for any query), creating the query, and executing the query. The editor makes a brief introduction to the implementation of LINQ query statements from these three aspects.

Example:

Class IntroToLINQ {static void Main () {/ / get the data source (which is served by an array here) int [] numbers = new int [7] {0lle 1je 2je 3je 4lt 5lc 6}; / / create a query (numQuery is of IEnumerable type) var numQuery = from num in numbers where (num%2) = = 0 select num / / execute query foreach (int num in numQuery) {Console.write ("{0jue 1}", num);}

Data sources that implement LINQ query statements:

In the above example, the data source is an array that implicitly supports generic IEnumerable (T) interfaces, while types that support IEnumerable (T) or derived interfaces are called "queryable types." So the array can be queried with LINQ.

If the data source does not already appear in memory as a queryable type, the LINQ provider must represent the data source in this way. For example, LINQ to XML loads an xml document into a queryable XElement type:

Using System.Xml.Linq XElement contacts = XElement.Load (@ "c:\ my.xml"); / / XElement represents a xml element

In LINQ to SQL, you must first create object-relational maps, and then write queries against those objects. LINQ handles communication between object queries and the database.

Using System.Data.Linq; DataContext db = new DataContext (@ "c:\ northwind.mdf")

Implement the creation query of LINQ query statement:

The query is first stored in the query variable and initialized with the query expression. This query variable does nothing and does not return data, but is only used to store the information necessary to generate results when the query is executed.

Implement the execution query of LINQ query statement:

The place where foreach is used in the above example is where the query results are retrieved, which is not executed until it is created, so it is called deferred execution, and num saves the returned values.

When an aggregate function query is needed, it is enforced to be executed immediately

Var numQuery = from num in numbers where (num%2) = = 0 select num; int evenNumCount = evenNumCount.Count ()

If a normal query needs to be executed immediately, you can call the ToList () or ToArray () method after the query statement.

The above is how to implement the LINQ query statement, the editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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