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This article is about how LINQ queries the database. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

You can use LINQ to write query access information for a variety of data sources. You don't have to use SQL syntax anymore, because LINQ provides the c # language for processing and provides the same type and expression capabilities. This is important because like a LINQ provides a declarative method that allows you to write more object-oriented programs.

You can use LINQ to write C # code that lists querying databases using LINQ and creating XML documents:

Var contacts / / retrieve customer table from customer in db.Customers where customer.Name.StartsWith ("A") & & customer.Orders.Count > 0 orderby customer.Name select new {customer.Name, customer.Phone}; var xml / / generate XML data new XElement ("contacts", from contact in contacts select new XElement ("contact", new XAttribute ("name", contact.Name), new XAttribute ("phone", contact.Phone)) from the customer list

The meaning of this code is to extract data from the database and create an XML document from it to write to the desired content. You will feel easier and more natural with LINQ. You'll see more LINQ queries soon, but for now it's focused on the language. With the from, where, orderby, and select keywords in the table, it is clear that they have been extended into the c# LINQ tool.

What we just showed is the C # code, but LINQ provides a common query architecture across programming languages. He works on C # 3.0 and VB.NET 9.0 (that is, VB 2008), so he needs a dedicated compiler, but it can be ported to other .NET languages. For now, F# already has LINQ capabilities, and more .NET languages will be supported by LINQ in the future.

The query in the figure uses the C # syntax rather than the new language. LINQ is not a new language. It is integrated into C # and VB.NET. In addition, LINQ can be used to avoid confusion between .NET programming languages and SQL, XSL, or other data-specific languages. LINQ enables queries to be stored in language-specific extension sets of programming languages through multiple types of data. You can think of linq as universal remote control. Sometimes you use it to query the database; in other ways, you can query XML documents as well. You just need to use your favorite programming language without switching to a query language such as SQL or XQuery.

We only provide you with a brief description of the LINQ query database. The question at this point is: why do we want to use tools like LINQ? Why not use other tools before? LINQ is created in program syntax as well as in relational databases and XML documents.

The fact that LINQ comes from a project is a simple fact: it is used in applications to drive and connect to databases. Therefore, knowing only one c # language in an application cannot satisfy your needs, and you also need to learn other languages, such as SQL syntax, together with C # to form the API of a complete application.

We will first look at a piece of data access code that uses the standard .NET API. We will point out the common problems encountered in this kind of code. Then we will show how these exist problems with other types of data such as XML. You will see general mismatches of data sources between LINQ addresses and programming language extensions to our analysis.

Thank you for reading! This is the end of the article on "how to query the database in LINQ". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it out for more people to see!

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