如何：对查询结果分页（实体框架）
本主题介绍如何对查询结果分页。 本示例先跳过查询结果（按 Product.ListPrice 排序）中的前三个 Product 对象，然后获取五个对象。 将使用以下每种实体框架查询技术说明同一示例：
LINQ to Entities
Entity SQL 以及 ObjectQuery<T>
ObjectQuery<T> 的查询生成器方法
本主题中的示例基于 Adventure Works 销售模型。若要运行本主题中的代码，则必须已经将 Adventure Works 销售模型添加到了您的项目中，并且已经将项目配置为使用实体框架。有关更多信息，请参见如何：使用实体数据模型向导（实体框架）或如何：手动配置实体框架项目和如何：手动定义实体数据模型（实体框架）。
示例
这是 LINQ to Entities 示例。
Using context As New AdventureWorksEntities
'LINQ to Entities only supports Skip on ordered collections.
Dim products As IOrderedQueryable(Of Product) = _
context.Products.OrderBy(Function(p) p.ListPrice)
Dim allButFirst3Products As IQueryable(Of Product) = products.Skip(3)
Console.WriteLine("All but first 3 products:")
For Each product As Product In allButFirst3Products
Console.WriteLine("Name: {0} \t ID: {1}", _
product.Name, _
product.ProductID)
Next
End Using
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
// LINQ to Entities only supports Skip on ordered collections.
IOrderedQueryable<Product> products = context.Products
.OrderBy(p => p.ListPrice);
IQueryable<Product> allButFirst3Products = products.Skip(3);
Console.WriteLine("All but first 3 products:");
foreach (Product product in allButFirst3Products)
{
Console.WriteLine("Name: {0} \t ID: {1}",
product.Name,
product.ProductID);
}
}
这是 Entity SQL 示例。
Using context As New AdventureWorksEntities()
' Create a query that takes two parameters.
Dim queryString As String = "SELECT VALUE product FROM AdventureWorksEntities.Products AS product " & _
" order by product.ListPrice SKIP @skip LIMIT @limit"
Dim productQuery As New ObjectQuery(Of Product)(queryString, context)
' Add parameters to the collection.
productQuery.Parameters.Add(New ObjectParameter("skip", 3))
productQuery.Parameters.Add(New ObjectParameter("limit", 5))
' Iterate through the collection of Contact items.
For Each result As Product In productQuery
Console.WriteLine("ID: {0}; Name: {1}", result.ProductID, result.Name)
Next
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Create a query that takes two parameters.
string queryString =
@"SELECT VALUE product FROM
AdventureWorksEntities.Products AS product
order by product.ListPrice SKIP @skip LIMIT @limit";
ObjectQuery<Product> productQuery =
new ObjectQuery<Product>(queryString, context);
// Add parameters to the collection.
productQuery.Parameters.Add(new ObjectParameter("skip", 3));
productQuery.Parameters.Add(new ObjectParameter("limit", 5));
// Iterate through the collection of Contact items.
foreach (Product result in productQuery)
Console.WriteLine("ID: {0}; Name: {1}",
result.ProductID, result.Name);
}
这是查询生成器方法示例。
Using context As New AdventureWorksEntities()
' Define the parameters used to define the "page" of returned data.
Dim skipValue As Integer = 3
Dim limitValue As Integer = 5
' Define a query that returns a "page" or the full
' Product data using the Skip and Top methods.
' When Top() follows Skip(), it acts like the LIMIT statement.
Dim query As ObjectQuery(Of Product) = _
context.Products.Skip("it.ListPrice", "@skip", _
New ObjectParameter("skip", skipValue)).Top("@limit", New ObjectParameter("limit", limitValue))
' Iterate through the page of Product items.
For Each result As Product In query
Console.WriteLine("ID: {0}; Name: {1}", result.ProductID, result.Name)
Next
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Define the parameters used to define the "page" of returned data.
int skipValue = 3;
int limitValue = 5;
// Define a query that returns a "page" or the full
// Product data using the Skip and Top methods.
// When Top() follows Skip(), it acts like the LIMIT statement.
ObjectQuery<Product> query = context.Products
.Skip("it.ListPrice", "@skip",
new ObjectParameter("skip", skipValue))
.Top("@limit", new ObjectParameter("limit", limitValue));
// Iterate through the page of Product items.
foreach (Product result in query)
Console.WriteLine("ID: {0}; Name: {1}",
result.ProductID, result.Name);
}
另请参见
参考
SKIP (Entity SQL)
LIMIT (Entity SQL)
Skip
Top