How to Efficiently Retrieve a Random Row with Conditions Using Linq to SQL?

LINQ to SQL conditions High -efficiency random retrieval data line

The use of Linq to SQL to query the database is a powerful way to retrieve relational database data. However, when applying specific conditions, you can bring some challenges when you choose a random line. This article discusses a solution to this problem efficiently.

Using analog user custom function (UDF)

Linq to SQL has no direct way to choose random line. To overcome this limit, a simulation UDF can be created in the database. This can be achieved by adding a method to some data contexts, as shown below:

This UDF acts as a placement to enable random sorting in SQL Server.

<code class="language-csharp">partial class MyDataContext {
     [Function(Name="NEWID", IsComposable=true)] 
     public Guid Random() 
     { // 证明我们的C#代码未使用... 
         throw new NotImplementedException(); 
     }
}</code>

Apply random sorting

Once the simulation UDF is in place, you can sort the Linq query by calling the method. This will indicate that the database uses the function to perform random sorting.

This query will retrieve a single random line that meets the specified conditions. ctx.Random() NEWID() Performance precautions

<code class="language-csharp">var cust = (from row in ctx.Customers
           where row.IsActive // 你的筛选条件
           orderby ctx.Random()
           select row).FirstOrDefault();</code>

It should be noted that using this UDF method may affect the performance of large tables. In this case, a more effective method is to determine the number of lines (using the

method), generate a random index, and then use the

and methods to search random lines.

The counting method

Count() Skip()

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