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This article is organized from the msdn
I. Concepts of LINQ:LINQ is short for Language Integrated Query (Language integration query), which is integrated in. netProgramming LanguageThis allows the query expression to get a good syntax check during compilation, rich metadata, and advantages of smart sensing for other strong languages. net Framework Version 3.5 i
method for creating a specific type of Expression directory tree node, for example, ParameterExpression (indicating a named parameter Expression) or MethodCallExpression (indicating a method call ). The root of the Expression directory tree generated by the compiler is always in the node of Type Expression
The following examples describe how to use the expression directory tree to create a dynamic LINQ query
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 othe
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
Label: = new Northwindcontext ())
{
var= 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 specified field var = context. Products
. Select =
be negative interop_db.SubmitChanges (); nwindTxn. commit ();} catch (Exception e) {// if there is an error, all operations roll back the Console. writeLine (e. message);} nwindConn. close ();
Statement Description: This example uses an existing ADO. NET connection to create a Northwind object, and then shares an ADO. NET transaction with this object. This transaction is used to execute SQL commands through the ADO. NET connection and submit changes
may also think about this. Add a filter condition "Nothing more" to add a parameter to the interface, a parameter to the stored procedure, and a condition to the WHERE clause ,...... Working hard.
The customer's filtering condition is as follows: since the order contains the "country" field, you want to filter the condition according to the country, and you can select multiple countries, for example:
The engineer may fall down when he sees the figure ......
The above can be used as a j
filter condition "Nothing more" to add a parameter to the interface, a parameter to the stored procedure, and a condition to the WHERE clause ,...... Working hard.
The customer's filtering condition is as follows: since the order contains the "country" field, you want to filter the condition according to the country, and you can select multiple countries, for example:
The engineer may fall down when he sees the figure ......
The above can be used as a joke, but in other words, there is no uni
Directory
[10 days to learn about Linq to SQL] day 1-Basic Knowledge
[10 days to learn about Linq to SQL] The next day -- data context
[10 days to learn about Linq to SQL] The third day -- Data
How can I convert Oracle queries to queries in the SQL database? The following describes how to convert an Oracle query to an SQL query. If you are interested in Oracle query, take a lo
Just a little bit of Linq was attracted by it, and I suddenly came up with the idea of learning and using it in one breath. So I posted a video on the ASP. NET official website. I am not very good at English, but I can understand how to use it. Below I wrote a little bit of fur I learned. It is a learning record.
First, I use Visual Studio 2008 development tools and SQL Server data sources, which are writte
Label:Recently doing projects using LINQ in conjunction with EntityFramework to handle database operations. Want to also use for almost a year, found that some use of skills is necessary to pay attention to, special to do under the summary, I hope that the new friends are helpful. At the beginning of the use of the total loop query subquery, the results of poor performance is not good, now look at all feel
3 courses. SelectAVG (degree) fromScorewhereCNO like'3%'GROUP BY Cno have Count (*) >=5Linq: fromSinchScoreswhereS.cno. StartsWith ("3") group S by s.cno into CCwhereCc. Count () >=5
SelectCc. Average (c =C.degree) Lambda:Scores.Where (S= = S.cno. StartsWith ("3") )
. GroupBy (S=s.cno). Where (CC= = (CC. Count () >=5) )
. Select (CC= CC. Average (c =C.degree)) Linq:sqlmethod like can also write: S.cno. StartsWith ("3") or Sqlmethods.like (S.cno,"%3") 14. Mult
") View Code 12. Grouping example Code queries the average score of at least 5 students in the score table and 3 courses. SelectAVG (degree) fromScorewhereCNO like'3%'GROUP BY Cno have Count (*) >=5Linq: fromSinchScoreswhereS.cno. StartsWith ("3") group S by s.cno into CCwhereCc. Count () >=5
SelectCc. Average (c =C.degree) Lambda:Scores.Where (S= = S.cno. StartsWith ("3") )
. GroupBy (S=s.cno). Where (CC= = (CC. Count () >=5) )
. Select (CC= CC. Average (c =C
This document uses the customers and orders tables in the northwind database as examples to illustrate how to query and add a table in the LINQ to SQL statement.
First, create datacontext and the corresponding entity class through the LINQ to SQL file wizard. If you do not k
LINQ to SQL can query SQL-based data quickly, including the basic object/relation mapper directly in VS, and the O/R mapper can quickly map SQL-based data sources to CLR objects and then use LINQ queries. In the project, right-cli
Linq to SQL: Second of integrated database language query
Step 5: Create Your Object Model1. Open the Data Connections Tree View2. Expand the Northwind folder3. Expand the Tables folder4. Double-click solution explorer to open the Northwind. dbml file.5. Drag the MERs table from the table folder to the Linq to
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