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This article mainly introduces "how to solve the problem of LINQ query operation". In daily operation, I believe many people have doubts about how to solve the problem of LINQ query operation. Xiaobian consulted all kinds of materials and sorted out simple and easy operation methods. I hope to help you answer the doubts of "how to solve the problem of LINQ query operation"! Next, please follow the small series to learn together!

Language Integrated Query (LINQ) is a breakthrough innovation in Visual Studio 2008 and the. NET Framework version 3.5 that bridges the object and data domains.

Traditionally, queries against data have been expressed as simple strings without compile-time type checking or IntelliSense support. In addition, you must learn different query languages for various data sources: SQL databases, XML documents, various Web services, and so on. LINQ makes queries a first-class language construct in C#and Visual Basic. You can write queries against collections of strongly typed objects using language keywords and familiar operators. An incomplete LINQ query written in C#against SQL Server databases with full type checking and IntelliSense support.

LINQ query operations consist of three operations:

Get data sources: All objects that support the generic IEnumerable(Of (T)) interface can be used as LINQ data sources, including Array, List, etc.

Create a query: Specify what information to retrieve from the data source, and you can also specify how to sort, group, or structure the information before returning it. Created (defined) queries are usually stored in variables and are not executed immediately upon definition but later. So remember: query variables themselves do not perform any operations and do not return any data, they just store query definitions.

3. Execute query: There are two cases of executing query, 1 is delayed execution;2 is immediate execution.

3.1 Delay execution: query definition and save in the query definition variables, not immediately executed, but in the subsequent need to execute. This usually requires using a For Each loop (which returns a sequence of values) or applying standard query operators. For value sequences, the retrieved data can be accessed using the iteration variable (number in the previous example) in the For Each loop.

3.2 immediate execution: In immediate execution, the query is executed as it is defined. Execution is triggered when a method is applied that requires access to individual elements of the query result. Immediate execution is usually enforced using one of the standard query operators that returns a single value. Count, Max, Average, and First are standard query operators. These standard query operators execute queries as soon as they are applied to evaluate and return single-instance results. For example:

Dim numbers = (From num In numbers _ Where num Mod 2 = 0 _ Select num).Count()

You can also enforce queries by calling the ToList or ToArray methods on queries (immediate execution) or query variables (delayed execution), as shown in the following code:

Dim evensList = (From num In numbers _ Where num Mod 2 = 0 _ Select num).ToList() At this point, the study of "how to solve the problem of LINQ query operation" is over, hoping to solve everyone's doubts. Theory and practice can better match to help everyone learn, go and try it! If you want to continue learning more relevant knowledge, please continue to pay attention to the website, Xiaobian will continue to strive to bring more practical articles for everyone!

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