linq to mysql

Label: style blog color AR for strong SP Div on The element operator returns a single specified element from a sequence. 1. defaultifempty The defaultifempty operator replaces an empty set with a set containing the default single value. When the returned sequence is empty and some objects need to be returned, a default value can be returned through this operator. 1>. Prototype Definition Public StaticIqueryable ThisIqueryable Public StaticIqueryable ThisIqueryable 2>. Example VaRExpr =F

Entity QueryPublic ienumerable{if (where = = null)Return this._db. Set//这个最重要.否则会出如题的错误.Return this._db. Set}//Solve the problem: Where () First use asexpandable ()/ 这个最重要.否则会出如题的错误. /LINQ to Entities does not support LINQ expression node type "Invoke"

operation. 17 18 Interop_db.transaction = Nwindtxn; // Add a transaction to datacontext 19 20 Product prod1 = Interop_db.products 21 . First (P => P. productid = 4 ); 22 Product prod2 = Interop_db.products 23 . First (P => P. productid = 5 ); 24 Prod1.unitsinstock -= 3 ; 25 Prod2.unitsinstock -= 5 ; 26 27 Interop_db.submitchanges (); // perform the operation 28 29 Nwindtxn. Commit ();

Overview:LINQ to XML (hereinafter referred to as LTX) is Microsoft's curd for XML based on LINQ technology. It is easier to use than the XML operation in System.Xml. This time use it in the company upgraded the boss's mail system, quite a bit of experience, now summed up.Main objects:1.xdocument:xml Document object loaded in XML document according to its static method: XDocument XDoc = Xdocument.load (@ "**xml path * *"). Element ("NodeName") obtains

A few small examples of linq and a small example of linq Private void button#click (object sender, EventArgs e) {int [] numbers = new int [7] {0, 1, 2, 3, 4, 5, 6 }; var result0 = from num in numbers where (num % 2 = 0) select num; foreach (int n in result0) {listBox1.Items. add (n) ;}} private void button2_Click (object sender, EventArgs e) {listBox1.Items. clear (); int [] numbers = new int [7] {2, 3, 4,

Source: http://www.cnblogs.com/li-peng/ Table before conversion: Converted table: Detailed descriptions are provided in the Code, Some other parameters are available below Using System;Using System. Collections. Generic;Using System. Data;Using System. Linq;Using System. Text;Namespace ConvertToTable{Class Program{Static void Main (string [] args){# Add a table to regionDataTable _ dt = new DataTable ();_ Dt. Columns. Add (new DataColumn ("staff_id"

Tags: style blog color ar for strong SP div on1. Query all fieldsusing New Northwindcontext ()) { var expr = context. Products; foreach (var in expr) { Console.WriteLine (item. ProductName);} }SELECT [Extent1].[ProductID] as [ProductID], [Extent1].[CategoryID] as [CategoryID], [Extent1].[ProductName] as [ProductName], [Extent1].[UnitPrice] as [UnitPrice], [Extent1].[discontinued] as [discontinued] from [dbo].[Product] as [Extent1]2. Querying a sp

1. Case when ... Then ...var from inch context. Products Selectnew { = P.productid, = p. ProductName, 0" Yes " " no " };SELECT [Extent1].[ProductID] as [ProductID], [Extent1].[ProductName] as [ProductName], Case when([Extent1].[UnitsInStock] > 0) ThenN'is a' ELSEN'No' END as [C1] from [dbo].[Product] as [Extent1]LINQ series:

Add an alias to a field in linq, and add an alias to a field in linq Linq is a form that we often use in queries. For example, we create a class, and then List Public class Modeltest {string id; public string Id {get {return id;} set {id = value ;}} string pwd; public string Pwd {get {return pwd ;} set {pwd = value ;}} string name; public string Name {get {retur

Tags: des style blog http io color ar OS usageThe DataTable. Select () method uses a filter syntax similar to SQL to extract records of interest from the DataTable. Although Select () can work well, it still has some obvious restrictions. First, it is string-based, that is, possible errors cannot be found during compilation. Secondly, its filtering function is very limited, and it does not provide other features that the LINQ operator can provide, suc

Part of this article is organized from MSDN First, the Concept of LINQ: LINQ is the abbreviation for Language Integrated query (language integration queries), which is integrated in the. NET programming language, which makes query expressions good at compile-time syntax checking, rich metadata, IntelliSense, and other strongly typed languages. Linq is a groundb

Let's go on to the LINQ to SQL statement, which we'll talk about group by/having operators and Exists/in/any/all/contains operators.Group by/having operatorScenario : grouping data to narrow the scope for us to find data.Description : An enumerable object that is assigned and returned after a group operation on an incoming parameter. To group or delay1. Simple form:var q = from p in db. Products Group p by P.categoryid into G select G;Stateme

].[ProductName], [t0].[Quantity],[t0].[CustomerName] FROM [dbo].[Invoices] AS [t0]WHERE [t0].[ShipCity] = @p0-- @p0: Input NVarChar (Size = 6; Prec = 0; Scale = 0) [London]Query: Id ing form The following example shows the orders for each quarter. var q = from qo in db.Quarterly_Orders select qo; The SQL statement is: SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[City],[t0].[Country] FROM [dbo].[Quarterly Orders] AS [t0]Inheritance support Supports single-Table ing. The entire inheri

This article is a summary of a very important part of LINQ, namely, LINQ to entities. It can be used to query databases without writing any data access code. Using LINQ to entities is very simple, and most of them are visualized operations. The detailed steps are as follows:Step 1: create a data model: 1. Right-click "app_code" and select Add project. In the new

Document directory Group by/having Operator Exists/In/any/all/contains operator Any All Contains We will continue to explain the LINQ to SQL statements. In this article, we will discuss the Group by/having operators and the exists/In/any/all/contains operators.Group by/having Operator Applicable scenarios: Grouping data. narrow down the scope of data for us. Description: Assigns and returns the enumerated objects after grouping the input para

. processflag = ' N ' ;Entity. Qty = Int . Parse (Q. qty );Listentity. Add (entity );}DB. maucpo. insertallonsubmit (listentity );DB. submitchanges ();}} First, you need to convert the input able to the enumerable type to execute the LINQ query. Here, the where condition is to filter out empty rows in the datatable, the content in the SELECT statement is to retrieve the data of the corresponding column in the able, convert the

ArticleDirectory Count/sum/MIN/max/AVG Operator 1. Common query: VaR q = from CInDB. Customers where c. City ="London"Select C. contactname; Note: Select must be placed behind DB. MERs Mers is the data source C is one of the customers arrays. Where Condition Statement Select returned content. For example, select C. contactname indicates that all qualified contactnames are returned. 2. SQL in-like queries PublicIqueryable InGetquery () Where IDs.

I have shared the problem of expression conversion in my previous article (Linq to Entity experience: expression conversion). I thought the problem was solved, but I found that the problem was not solved in actual application, it is not completely unsolved, but not practical. The problem is as follows:Let's take a look at the problem.Objective of expression Conversion: In fact, we are so difficult to convert expressions to convert the Expression Tree

[Linq] common syntax summary and linq Summary Language inheritance Query(Language Integrated Query, LINQ). in C # programming Language, the Query syntax is Integrated, and different data sources can be accessed using the same syntax. LINQ provides an abstraction layer for different data sources, so you can use the same

2 points:A collection of 1.LINQ operations must implement the IEnumerable interface, so that a collection that implements the interface before 3.0 is converted to a LINQ collection by either the cast or the TypeOf method;2. Query and lame the expression can be used together. Which is convenient to use, they only when the first use of the real query; List　　LINQ