LINQ C# (Wie es für Entwickler funktioniert)

LINQ Query Syntax

LINQ Query Syntax is an expressive and readable way to write queries. It is designed to be familiar to those with a background in SQL and SQL databases, making the transition to LINQ queries smooth. This syntax involves using LINQ query expressions that closely resemble SQL queries.

For instance, you would use keywords like from, select, and where to form readable and concise LINQ query syntax to retrieve data from a collection.

Method Syntax in LINQ

LINQ offers method syntax, a more flexible and powerful alternative, along with the traditional query syntax, using extension methods and lambda expressions.

This syntax is especially useful for writing complex LINQ queries and performing advanced query operations. Method syntax can be more concise in specific scenarios and offers the full power of LINQ's querying capabilities.

The Basics of LINQ Queries

To effectively write LINQ queries, it's essential to understand the concept of a query variable. This variable is where the results of a LINQ query expression are stored. LINQ can work with any data source that implements the IEnumerable<T> interface, making it highly versatile.

For example, when working with data collections, you can easily apply LINQ queries to perform various operations like filtering and sorting.

using System;
using System.Collections.Generic;
using System.Linq;

public class Example
{
    public static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6 };

        // LINQ query using query syntax to filter even numbers
        var evenNumbersQuery = from num in numbers
                               where num % 2 == 0
                               select num;

        Console.WriteLine("Even numbers using query syntax:");
        foreach (var num in evenNumbersQuery)
        {
            Console.WriteLine(num);
        }

        // LINQ query using method syntax to filter even numbers
        var evenNumbersMethod = numbers.Where(num => num % 2 == 0);

        Console.WriteLine("Even numbers using method syntax:");
        foreach (var num in evenNumbersMethod)
        {
            Console.WriteLine(num);
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;

public class Example
{
    public static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6 };

        // LINQ query using query syntax to filter even numbers
        var evenNumbersQuery = from num in numbers
                               where num % 2 == 0
                               select num;

        Console.WriteLine("Even numbers using query syntax:");
        foreach (var num in evenNumbersQuery)
        {
            Console.WriteLine(num);
        }

        // LINQ query using method syntax to filter even numbers
        var evenNumbersMethod = numbers.Where(num => num % 2 == 0);

        Console.WriteLine("Even numbers using method syntax:");
        foreach (var num in evenNumbersMethod)
        {
            Console.WriteLine(num);
        }
    }
}

Imports System
Imports System.Collections.Generic
Imports System.Linq

Public Class Example
	Public Shared Sub Main()
		Dim numbers As New List(Of Integer) From {1, 2, 3, 4, 5, 6}

		' LINQ query using query syntax to filter even numbers
		Dim evenNumbersQuery = From num In numbers
			Where num Mod 2 = 0
			Select num

		Console.WriteLine("Even numbers using query syntax:")
		For Each num In evenNumbersQuery
			Console.WriteLine(num)
		Next num

		' LINQ query using method syntax to filter even numbers
		Dim evenNumbersMethod = numbers.Where(Function(num) num Mod 2 = 0)

		Console.WriteLine("Even numbers using method syntax:")
		For Each num In evenNumbersMethod
			Console.WriteLine(num)
		Next num
	End Sub
End Class

Transforming Data with LINQ

LINQ excels in its ability to transform data. With various query operations, you can manipulate data in numerous ways. Whether converting data types, filtering collections based on certain criteria, or aggregating data for summaries, LINQ provides a comprehensive suite of tools to transform data as required.

LINQ to SQL and Relational Databases

One of the most popular uses of LINQ is with SQL and relational databases. LINQ to SQL simplifies interacting with databases by allowing you to perform SQL-like queries directly on the database tables as if they were in-memory data structures.

This reduces the amount of boilerplate code and makes database operations more intuitive and less error-prone.

Querying XML Documents and More

LINQ is not limited to relational databases. It is equally adept at handling XML documents, offering a straightforward way to query and manipulate XML data.

With LINQ to XML, parsing and querying XML files become simpler and more intuitive, as you can use familiar LINQ query syntax to interact with XML elements and attributes.

IronPDF

IronPDF Library for PDF Manipulation is a library in the Iron Software Suite that enables C# developers to create, read, and edit PDF files. Developers can efficiently manipulate data and render it into PDF format when combined with LINQ.

For instance, you could use LINQ queries to retrieve data from a database or an XML document and then use IronPDF to generate a well-formatted PDF report from the queried data.

IronOCR

IronOCR Optical Character Recognition Tool is another valuable tool in the suite, offering Optical Character Recognition (OCR) capabilities. It can be used to convert images to text in over 125 languages.

In a typical use case, developers might use LINQ to process and filter a collection of image paths, and then apply IronOCR to extract text from these images, effectively combining data retrieval and text extraction in a streamlined process.

IronXL

IronXL Excel Processing Library focuses on working with Excel files without the need for Office Interop. It's particularly useful when working with data in Excel format.

With LINQ, developers can query and transform data from various sources and then use IronXL to export this data to Excel spreadsheets for reporting, further analysis, or distribution.

IronBarcode

IronBarcode for Barcode and QR Code Generation library is used for reading and writing barcodes and QR codes. It can be integrated with LINQ to process large datasets, identifying or generating barcodes or QR codes based on data retrieved or processed using LINQ queries.