Linq to sql（九）：其它补充(二)

已编译查询

       对于一些在项目中经常被用到的查询可以封装成已编译查询，这样就能提高执行效率：

static class Queries

{

    public static Func<NorthwindDataContext, string, IQueryable<Customer>>

        CustomersByCity = CompiledQuery.Compile((NorthwindDataContext ctx, string city) => from c in ctx.Customers where c.City == city select c);

}

       调用查询方式如下：   

        GridView1.DataSource = Queries.CustomersByCity(ctx, "London");

        GridView1.DataBind();

获取一些信息

        var query = from c in ctx.Customers select c;

        Response.Write("Provider类型：" + ctx.Mapping.ProviderType + "<br/>");

        Response.Write("数据库：" + ctx.Mapping.DatabaseName + "<br/>");

        Response.Write("表：" + ctx.Mapping.GetTable(typeof(Customer)).TableName + "<br/>");

        Response.Write("表达式：" + query.Expression.ToString() + "<br/>");

        Response.Write("sql：" + query.Provider.ToString() + "<br/>");

  上面的代码执行结果如下：

Provider类型：System.Data.Linq.SqlClient.SqlProvider
数据库：Northwind
表：dbo.Customers
表达式：Table(Customer).Select(c => c)
sql：SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] FROM [dbo].[Customers] AS [t0]