Shulou(Shulou.com)06/02 Report--

This article mainly explains "What is the role of Linq". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let Xiaobian take you to learn "what role Linq has"!

Learn Linq

In our software, the importance of data is indescribable, especially such business applications as ERP, CRM, etc., which revolve around data; however, data comes from a variety of sources, such as business objects stored in memory, data stored in xml files, SqlServer relational database... These data sources have different read operations and are not easy to convert to each other; VS. Net provides various technologies to support the operation of these data sources, such as ADO. Net for manipulating databases and API for manipulating xml files.(XmlDocument, XmlReader, XPathNavigator, etc.), as well as some operations on data stored in memory (arrays, parameter variables, classes, generics, etc.); now in C#3.0 provides a new technology to integrate various data manipulation problems, this is Linq;

Linq aims to achieve deep integration of language and data, Linq accesses various data sources in a unified way, reads data in the same way, queries like SQL statements, and these are integrated into familiar programming languages such as C#, VB, and Linq uses strong typing, and provides compile-time checking and VS intelligence-aware features.

Below we take SQL Server as the data source and list a piece of code to analyze:

// ADO. NET we will use it to provide SqlConnection, SqlCommand,

SqlDataAdapter, SqlReader, DataSet, DataTable, etc. to access operational databases;

//Fill DataSet with SqlDataAdapter

using (SqlConnection conn = new SqlConnection(""))

{

DataSet ds = new DataSet();

SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM Customers", conn);

da.Fill(ds);

}

//read data using SqlDataReader

using (SqlConnection connection = new SqlConnection(""))

{

connection.Open();

SqlCommand command = connection.CreateCommand();

command.CommandText = @"SELECT Name, Country FROM Customers WHERE City = @City";

command.Parameters.AddWithValue("@City", "Paris");

using (SqlDataReader reader = command.ExecuteReader())

{

while (reader.Read())

{

string name = reader.GetString(0);

string country = reader.GetString(1);

}

}

}

In this code, we are just a simple data read, whether using SqlDataAdapter or SqlDataReader will encounter some problems:

1. If you write statements directly in the code, you cannot ensure the correctness of the statements, and even the keywords of the basic SQL statements cannot guarantee whether they are written correctly; and in Linq, some commonly used keywords such as Select, from, where, etc. are written as extension methods to ensure that statements are verified at compilation time;

2. The parameters used in the query, and the results returned by the query are weak types, and in our object-oriented programming, we hope to use strong types to ensure that our program is correct, so we need a lot of auxiliary judgment to ensure that the parameters we pass and the results we get meet the corresponding type requirements; while we use strong types in Linq to avoid these redundant judgments and ensure that the program can be verified by the compiler and will not wait until runtime to catch errors;

3.*** The problem with this code is that it only works with SQL Server, and if you use other databases (Oracle, MySQL...), or other data sources (xml, text files...) It will change a lot, or rewrite the method to use, and using Linq can effectively avoid these problems.

At this point, I believe everyone has a deeper understanding of "what Linq does". Let's actually operate it! Here is the website, more related content can enter the relevant channels for inquiry, pay attention to us, continue to learn!

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