linq面试问题 [英] linq interview questions

问题描述

你在.net项目中使用linq的地方？

where do you use linq in .net projects?

推荐答案

LINQ可以在C＃或Visual Basic .NET程序中的任何地方使用，其中可以声明变量。



请参阅关于LINQ的维基百科文章：

LINQ提供了查询数据的功能，可以方便地从数组，可枚举类，XML文档，关系数据库和第三方数据源中提取和处理数据。



请参阅Microsoft的 LINQ文档 。

LINQ can be used anywhere within a C# or Visual Basic .NET program where a variable can be declared.

See the Wikipedia article on LINQ:
LINQ provides the capability to query data to conveniently extract and process data from arrays, enumerable classes, XML documents, relational databases and third-party data sources.

See Microsoft's documentation of LINQ.

你可以使用许多领域linq一些例子是

您可以使用linq创建/修改/导航/遍历xml文档。您可以将其命名为linq to xml。

您可以使用linq搜索/排序/导航/过滤自定义对象层次结构，对象集合，列表比较，文件内容搜索，目录搜索等。您可以将它命名为linq to object。

您可以使用linq使用对象关系映射。您可以将其命名为linq to sql。

您可以使用linq访问/导航/过滤数据集。您可以将其命名为linq to dataset。

事先您可以为各种组件创建linq提供程序，轻松访问访问，从读取各种来源创建对象等。

There are many areas you can use linq some examples are
You can create/modify/navigate/traverse xml document using linq. You can call it linq to xml.
you can search/sort/navigate/filter custom object hierarchy, object collection, list compare, file content search, directory search etc using linq. You can call it linq to object.
You can use object relational mapping using linq. You can call it linq to sql.
You can access/navigate/filter dataset using linq. You can call it linq to dataset.
In advance you can create linq providers for various component easily access access, create object from read various sources etc.

什么是一个Lambda表达式？





Lambda表达式只是一个匿名函数，可以包含表达式和语句。 Lambda表达式主要用于创建委托或表达式树类型。 Lambda表达式使用lambda operator =>并读作'去'运算符。



此运算符的左侧指定输入参数，并包含右侧的表达式或语句块。

1.什么是语言集成查询（LINQ）？

LINQ是一种编程模型，它是通用标准查询运算符的组合，允许您处理数据，不管任何基于.NET的编程语言中的数据源。它是基于将查询功能集成到任何.NET语言中的一组技术的名称。

2.什么是LINQ查询表达式？

LINQ查询，也称为查询表达式，由查询子句的组合组成，用于标识查询的数据源。它包括有关排序，过滤，分组或连接以应用于源数据的说明。 LINQ查询表达式语法类似于SQL语法。它指定应从数据源检索哪些信息。

3.编写执行LINQ查询的基本步骤。

以下是执行a的三个基本步骤LINQ查询：

•获取数据源（数据源可以是SQL数据库或XML文件）

•创建查询

•执行查询

4.在Visual Basic和C＃中编写LINQ查询的基本语法。

在Visual Basic中，LINQ的基本语法查询以From子句开头，以Select或Group By子句结束。此外，您可以使用Where，Order By和Order By Descending子句来执行其他功能，例如过滤数据和按特定顺序生成数据。



在C＃中，LINQ查询的基本语法以From子句开头，以Select或group by子句结束。此外，您可以使用where，orderby和Orderby降序子句来执行其他功能，例如过滤数据和按特定顺序生成数据。

5. LINQ查询在哪个语句中执行？

LINQ查询在Visual Basic中的For Each语句和C＃中的foreach语句中执行。

6.在LINQ中，lambda表达式是许多标准查询运算符。它是对还是错？

7.什么是PLINQ？

PLINQ代表并行语言集成查询。它是LINQ的并行实现，其中可以使用多个处理器执行查询。 PLINQ确保执行环境中并行处理器上软件的可扩展性。它用于数据快速增长的地方，例如电信行业或数据异构的地方。



PLINQ还支持LINQ的所有运算符。此外，您可以使用PLINQ查询'集合。它还可以同时运行多个LINQ查询，并利用系统上的处理器。除此之外，PLINQ使用并行执行，这有助于快速运行查询。并行执行为PLINQ提供了对某些类型的遗留代码的主要性能改进，这需要花费太多时间来执行。

8.支持LINQ的Visual Basic功能有哪些？

Visual Basic包括支持LINQ的以下功能：

•匿名类型 - 允许您根据查询结果创建新类型。

•隐式类型变量 - 允许编译器在声明和初始化变量时推断并指定类型。

•扩展方法 - 使您可以使用自己的方法扩展现有类型，而无需修改类型本身。

9. LINQ查询中DISTINCT子句的功能是什么？

DISTINCT子句返回没有重复值的结果集。

10。什么是DataContext类以及它与LINQ有什么关系？

将LINQ to SQL Classes项添加到项目并打开O / R Designer之后，空设计冲浪ace表示准备配置的空DataContext类。 DataContext类是LINQ to SQL类，充当SQL Server数据库和映射到该数据库的LINQ to SQL实体类之间的管道。此类包含连接字符串信息以及用于连接到数据库和操作数据库中的数据的方法。它配置了拖动到设计图面上的第一个项目提供的连接信息。

11. Take和Skip子句有什么区别？

Take子句返回指定数量的元素。例如，您可以使用Take子句从数组中返回两个值。 Skip子句跳过查询中指定数量的元素并返回其余元素。例如，您可以使用Skip子句跳过字符串数组中的前四个字符串并返回剩余的字符串数组。

12.什么是对象关系设计器（0 / R设计器）？

0 / R设计器提供了一个可视化设计表面，用于创建基于数据库中对象的LINQ to SQL实体类和关联（关系）。

13.其中接口在LINQ中实现标准查询运算符？
标准查询运算符实现IEnumerable< t>或者IQueryable< t>在Visual Basic中的C＃和theIEnumerable（Of T）或IQueryable（Of T）接口中的接口。

14. LINQ中的标准查询运算符是什么？

标准查询LINQ中的运算符是构成LINQ模式的扩展方法。这些运算符形成一个API，可以查询任何.NET数组或集合。它对序列进行操作，允许您执行操作，例如确定序列中是否存在值以及执行聚合函数，例如序列上的求和。

15.关于什么参数， GroupBy子句对数据进行分组？

GroupBy子句对共享公共属性的元素进行分组。

16.什么是LinqDataSource控件？

LinqDataSource控件使您可以使用LINQ。在ASP.NET网页中通过设置标记文本中的属性。您可以使用控件检索或修改数据。它类似于SqIDataSource和ObjectDataSource控件，因为它可以用于声明性地将页面上的其他ASP.NET控件绑定到数据源。不同之处在于，不是直接绑定到数据库或泛型类，而是将LinqDataSource控件设计为绑定启用LINQ的数据模型。

17.如何打开O / R设计器？

您可以通过向项目添加新的LINQ to SQL Classes项来打开O / R设计器。

18.标准查询运算符本身就是一组扩展方法，为实现IEnumerable< t>的任何类型提供LINQ查询功能。 Visual Basic中的接口。它是对还是错？

19. LINQ中的lambda表达式是什么？

lambda表达式是一个没有名称的函数，可以计算并返回单个值。所有lambda表达式都使用lambda operator =>，它按原样读取。 lambda运算符的左侧指定输入参数，右侧包含表达式或语句块。

20.在使用LINQ to DataSet查询DataSet对象之前，必须首先填充数据集你怎么能这样做？

你可以使用不同的方法将数据加载到数据集中，例如：

•使用DataAdapter类

•使用LINQ to SQL

21. LINQ的不同实现是什么？

LINQ的不同实现是：

•LINQ to SQL - 指.NET Framework 3.5版的一个组件，它提供了一个运行时基础结构来管理作为对象的关系数据。

•LINQ to DataSet - 指的是一个让它变得更容易和更快的组件查询DataSet对象中缓存的数据。

•LINQ to XML - 提供内存中的XML编程接口。

•LINQ to Objects - 指使用LINQ查询任何IEnumerable或IEnumerable（T）集合直接，不使用中间LINQ提供程序或API，例如LINQ to SQL或LINQ to XML。

22.哪个命令行工具为LINQ生成代码和映射到.NET Framework的SQL组件？

SqlMetal.exe命令行工具生成代码并映射LINQ to SQL组件。

23.命名公开的控件LINQ通过ASP.NET数据源控件架构为Web开发人员提供了特性。

LinqDataSource控件通过ASP.NET数据源控件架构向Web开发人员公开LINQ功能。

24. LINQ中的Select子句和SelectMany（）方法有什么区别？

Select子句和SelectMany（）方法都用于从值源生成结果值。不同之处在于结果集。 Select子句用于为每个源值生成一个结果值。结果值是一个集合，其查询中的元素数量相同。相反，theSelectMany（）方法生成一个包含查询中的连接集合的结果。

What is a Lambda expression?


A Lambda expression is nothing but an Anonymous Function, can contain expressions and statements. Lambda expressions can be used mostly to create delegates or expression tree types. Lambda expression uses lambda operator => and read as 'goes to' operator.

Left side of this operator specifies the input parameters and contains the expression or statement block at the right side.
1. What is Language Integrated Query (LINQ)?
LINQ is a programming model that is the composition of general-purpose standard query operators that allow you to work with data, regardless of the data source in any .NET based programming language. It is the name given to a set of technologies based on the integration of query capabilities into any .NET language.
2. What are LINQ query expressions?
A LINQ query, also known as a query expression, consists of a combination of query clauses that identify the data sources for the query. It includes instructions for sorting, filtering, grouping, or joining to apply to the source data. The LINQ query expressions syntax is similar to the SQL syntax. It specifies what information should be retrieved from the data source.
3. Write the basic steps to execute a LINQ query.
The following are the three basic steps to execute a LINQ query:
• Obtain the data source (The data source can be either an SQL database or an XML file)
• Create a query
• Execute the query
4. Write the basic syntax of a LINQ query in Visual Basic as well as in C#.
In Visual Basic, the basic syntax of a LINQ query starts with the From clause and ends with the Select or Group By clause. In addition, you can use the Where, Order By, and Order By Descending clauses to perform additional functions, such as filtering data and generating the data in a specific order.

In C#, the basic syntax of a LINQ query starts with the From clause and ends with the Select or group by clause. In addition, you can use the where, orderby, and Orderby descending clauses to perform additional functions, such as filtering data and generating the data in a specific order.
5. In which statement the LINQ query is executed?
A LINQ query is executed in the For Each statement in Visual Basic and in the foreach statement in C#.
6. In LINQ, lambda expressions underlie many of the standard query operators. Is it True or False?
7. What is PLINQ?
PLINQ stands for Parallel Language Integrated Query. It is the parallel implementation of LINQ, in which a query can be executed by using multiple processors. PLINQ ensures the scalability of software on parallel processors in the execution environment. It is used where data grows rapidly, such as in telecom industry or where data is heterogeneous.

PLINQ also supports all the operators of LINQ. In addition, you can query 'collections by using PLINQ. It can also run several LINQ queries simultaneously and makes use of the processors on the system. Apart from this, PLINQ uses parallel execution, which helps in running the queries quickly. Parallel execution provides a major performance improvement to PLINQ over certain types of legacy code, which takes too much time to execute.
8. What are the different Visual Basic features that support LINQ?
Visual Basic includes the following features that support LINQ:
• Anonymous types - Enables you to create a new type based on a query result.
• Implicitly typed variables - Enables the compiler to infer and assign a type when you declare and initialize a variable.
• Extension method - Enables you to extend an existing type with your own methods without modifying the type itself.
9. What is the function of the DISTINCT clause in a LINQ query?
The DISTINCT clause returns the result set without the duplicate values.
10. What is the DataContext class and how is it related to LINQ?
After you add a LINQ to SQL Classes item to a project and open the O/R Designer, the empty design surface represents an empty DataContext class ready to be configured. The DataContext class is a LINQ to SQL class that acts as a conduit between a SQL Server database and the LINQ to SQL entity classes mapped to that database. This class contains the connection string information and the methods for connecting to a database and manipulating the data in the database. It is configured with connection information provided by the first item that is dragged onto the design surface.
11. What is the difference between the Take and Skip clauses?
The Take clause returns a specified number of elements. For example, you can use the Take clause to return two values from an array of numbers. The Skip clause skips the specified number of elements in the query and returns the rest. For example, you can use the Skip clause to skip the first four strings in an array of strings and return the remaining array of string.
12. What is Object Relational Designer (0/R Designer)?
The 0/R Designer provides a visual design surface to create LINQ to SQL entity classes and associations (relationships) that are based on objects in a database.
13. Which interface implements the standard query operators in LINQ?
The standard query operators implement the IEnumerable<t> or the IQueryable<t> interface in C# and theIEnumerable(Of T) or the IQueryable(Of T) interface in Visual Basic.
14. What are standard query operators in LINQ?
The standard query operators in LINQ are the extension methods that form the LINQ pattern. These operators form an API that enables querying of any .NET array or collection. It operates on sequences and allows you to perform operations, such as determining if a value exists in the sequence and performing an aggregated function, such as a summation over a sequence.
15. On what parameter does the GroupBy clause group the data?
The GroupBy clause groups the elements that share a common attribute.
16. What is a LinqDataSource control?
The LinqDataSource control enables you to use LINQ. in an ASP.NET Web page by setting the properties in the markup text. You can use the control retrieve or modify data. It is similar to the SqIDataSource andObjectDataSource controls in the sense that it can be used to declaratively bind other ASP.NET controls on a page to a data source. The difference is that instead of binding directly to a database or to a generic class, theLinqDataSource control is designed to bind a LINQ enabled data model.
17. How can you open the O/R Designer?
You can open the O/R Designer by adding a new LINQ to SQL Classes item to a project.
18. The standard query operators are themselves a set of extension methods that provide the LINQ query functionality for any type that implements the IEnumerable<t> interface in Visual Basic. Is it True or False?
19. What are lambda expressions in LINQ?
A lambda expression is a function without a name that calculates and returns a single value. All lambda expressions use the lambda operator =>, which read as goes to. The left side of the lambda operator specifies the input parameters and the right side holds the expression or statement block.
20. Before you query a DataSet object by using LINQ to DataSet, you must first populate the dataset How can you do this?
You can load the data into the dataset by using different methods, such as:
• Using the DataAdapter class
• Using LINQ to SQL
21. What are the different implementations of LINQ?
The different implementations of LINQ are:
• LINQ to SQL - Refers to a component of.NET Framework version 3.5 that provides a run-time infrastructure to manage relational data as objects.
• LINQ to DataSet - Refers to a component that makes it easier and faster to query over data cached in a DataSet object.
• LINQ to XML - Provides an in-memory XML programming interface.
• LINQ to Objects - Refers to the use of LINQ queries with any IEnumerable or IEnumerable(T)collection directly, without the use of an intermediate LINQ provider or API, such as LINQ to SQL or LINQ to XML.
22. Which command-line tool generates code and mapping for the LINQ to SQL component of .NET Framework?
The SqlMetal.exe command-line tool generates code and map the LINQ to SQL component.
23. Name the control that exposes the LINQ features to Web developers through the ASP.NET data-source control architecture.
The LinqDataSource control exposes the LINQ features to Web developers through the ASP.NET data-source control architecture.
24. What is the difference between the Select clause and SelectMany() method in LINQ?
Both the Select clause and SelectMany() method are used to produce a result value from a source of values. The difference lies in the result set. The Select clause is used to produce one result value for every source value. The result value is a collection that has the same number of elements from the query. In contrast, theSelectMany() method produces a single result that contains a concatenated collection from the query.

这篇关于linq面试问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！