LINQ (Language Integrated Query) is a feature in C# that provides a powerful and expressive way to query and manipulate data from different data sources, such as collections, databases, XML, and more. It allows you to write queries using a uniform syntax, regardless of the data source.
You can write LINQ queries in C# for SQL Server databases, XML documents, ADO.NET Datasets, and any collection of objects that supports IEnumerable or the generic IEnumerable
All LINQ query operations consist of three distinct actions:
Obtain the data source.
Create the query.
Execute the query. # The Query The query specifies what information to retrieve from the data source or sources. Optionally, a query also specifies how that information should be sorted, grouped, and shaped before it is returned. A query is stored in a query variable and initialized with a query expression. To make it easier to write queries, C# has introduced new query syntax.
Queries in LINQ specify what information to retrieve from the data source and can include filtering, sorting, and shaping operations. Queries are stored in query variables and are executed when iterated over in a foreach statement.
LINQ queries exhibit deferred execution, meaning that the actual execution and retrieval of data occur when the query variable is iterated over. However, immediate execution can be forced using methods like Count(), ToList(), or ToArray().
# The “Basic LINQ Query Operations” article provides an overview of common operations used in LINQ (Language Integrated Query) queries in C#.
Obtaining a Data Source: The article explains how to specify the data source for a LINQ query using the “from” clause and introduces the concept of a range variable.
Filtering: The “where” clause is used to apply Boolean expressions as filters to the data source, allowing the query to return only elements that satisfy the specified conditions.
Ordering: The “orderby” clause enables sorting the results of a query based on a specified property. The default comparer is used for sorting, but descending order can also be specified.
Grouping: The “group” clause allows grouping query results based on a specific key. The article demonstrates how to iterate over the grouped results and access the key and associated elements.
Joining: The “join” clause facilitates associating elements from two different sequences based on a common property. The article presents an example of joining customer and distributor data.
Selecting (Projections): The “select” clause determines the shape and type of the returned elements in the query results. It can include projections to transform data or create new objects.
Create a C# Project: create a console application project in Visual Studio, with the necessary references and using directives for LINQ.
Create an in-Memory Data Source: define a data source using a list of Student objects, showcasing features like auto-implemented properties and object/collection initializers.
Create the Query: write a query expression that filters the students based on a condition, such as scores on a test, using the “where” clause.
Execute the Query: a code to execute the query and iterate over the results using a foreach loop, printing the selected student information to the console.
Additional Query Operations: there are additional query operations like ordering results, grouping, introducing identifiers using “let” and using method syntax in query expressions.
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