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This article mainly explains "how to understand LINQ and ADO.NET technology". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to understand LINQ and ADO.NET technology.

LINQ and ADO.NET

Today, many business developers must use two (or more) programming languages: a high-level language for the business logic and presentation layer (such as Visual C # or Visual Basic) and a query language that can interact with databases (such as Transact-SQL). This requires developers to be proficient in multiple languages to be effective, and it also leads to language mismatches in the development environment. For example, an application that uses data access API to execute a query against a database specifies the query as a string enclosed in quotation marks. The compiler cannot read this query string, so it does not check for errors, such as invalid syntax or whether referenced columns or rows actually exist. The type of query parameter is not checked, and IntelliSense is not supported.

Language integrated queries (LINQ) enable developers to form set-based queries in application code without having to use a separate query language. You can write LINQ queries against a variety of enumerable data sources, that is, data sources that implement the IEnumerable interface, including data structures that reside in memory, XML documents, SQL databases, DataSet objects, and so on. Although these enumerable data sources are implemented in many ways, they all expose the same syntax and language constructs. Because you can use the programming language itself to form queries, you do not have to use other query languages embedded in strings that cannot be understood or verified by the compiler. Integrating queries into the programming language also makes Visual Studio programmers more efficient by providing compile-time type and syntax checking as well as IntelliSense. These features reduce the need for query debugging and error repair.

There are three independent ADO.NET languages that integrate query (LINQ) technologies: LINQ to DataSet, LINQ to SQL, and LINQ to Entities. LINQ to DataSet provides a variety of optimized queries against DataSet, LINQ to SQL allows you to query the SQL Server database schema directly, and LINQ to Entities allows you to query the entity data model.

Objects that transfer data from SQL tables to memory are often tedious and error-prone. The LINQ provider implemented by LINQ to DataSet and LINQ to SQL can transform source data into a collection of IEnumerable-based objects. When you query and update data, programmers always view the data in the form of IEnumerable collections. Provides full IntelliSense support for writing queries against these collections.

LINQ and ADO.NET: diagrams

The following diagram outlines how ADO.NET LINQ technology is associated with high-level programming languages and LINQ-enabled data sources.

The following sections provide more information about LINQ to DataSet, LINQ to SQL, and LINQ to Entities.

LINQ to DataSet

DataSet is a key element of the disconnected programming model from which ADO.NET is generated and is widely used. LINQ to DataSet enables developers to build richer query capabilities into DataSet by using the same query representation mechanism available from many other data sources.

LINQ to SQL

LINQ to SQL is a useful tool for developers who do not need to map to a conceptual model. By using LINQ to SQL, you can use the LINQ programming model directly on an existing database schema. LINQ to SQL enables developers to generate .NET Framework classes that represent data. These generated classes map directly to database tables, views, stored procedures, and user-defined functions, rather than to the conceptual data model.

When using LINQ to SQL, developers can write code for the storage schema directly using the same LINQ programming pattern as memory collections and DataSet, in addition to other data sources such as XML.

LINQ to Entities

Most applications are currently written on top of relational databases. Sometimes these applications will need to interact with data represented in relational form. Database architecture is not always an ideal choice for building applications, and the conceptual model of the application is different from the logical model of the database. An entity data model is a conceptual data model that can be used to model domain-specific data so that applications can interact with the data as objects.

Expose relational data as objects in the .NET environment through the entity data model. In this way, the object layer becomes an ideal target for LINQ support, allowing developers to write queries to the database in the language used to build business logic.

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