EF ObjectQuery查询及方法

 

string

esql =

"select value c from NorthwindEntities.Customers as c order by

c.CustomerID limit 10"

;

ObjectQuery

<

Customers

> query = edm.CreateQuery<

Customers

>(esql);

Console

.WriteLine(query.GetResultType().ToString());

//

输出结果为：

//NorthWindModel.Customers

}



ToTraceString

方法：

获取当前执行的

SQL

语句。



Where

实例代码如下：

using

(

var

edm =

new

NorthwindEntities

())

{

string

esql =

"select value c from NorthwindEntities.Customers as c "

;

ObjectQuery

<

Customers

> query1 = edm.CreateQuery<

Customers

>(esql);

//

使用

ObjectParameter

的写法

query1 = query1.Where(

"it.CustomerId=@customerid"

);

query1.Parameters.Add(

new

ObjectParameter

(

"customerid"

,

"ALFKI"

));

//

也可以这样写

//ObjectQuery<Customers> query2 = edm.Customers.Where("it.CustomerID='ALFKI'");

foreach

(

var

c

in

query1)

Console

.WriteLine(c.CustomerID);

//

显示查询执行的

SQL

语句

Console

.WriteLine(query1.ToTraceString());

}



First/ FirstOrDefault

实例代码如下：

using

(

var

edm =

new

NorthwindEntities

())

{

string

esql =

"select value c from NorthwindEntities.Customers as c order by

c.CustomerID limit 10"

;

 

ObjectQuery

<

Customers

> query = edm.CreateQuery<

Customers

>(esql);

Customers

c1 = query.First();

Customers

c2 = query.FirstOrDefault();

Console

.WriteLine(c1.CustomerID);

Assert

.IsNotNull(c2);

Console

.WriteLine(c2.CustomerID);

}



Distinct

实例代码如下：

using

(

var

edm =

new

NorthwindEntities

())

{

string

esql =

"select value c.City from NorthwindEntities.Customers as c order by

c.CustomerID limit 10"

;

ObjectQuery

<

string

> query = edm.CreateQuery<

string

>(esql);

query = query.Distinct();

foreach

(

string

c

in

query)

{

Console

.WriteLine(

"City {0}"

, c);

}

}



Except:

返回两个查询的差集。实例代码如下：

using

(

var

edm =

new

NorthwindEntities

())

{

string

esql1 =

"select value c from NorthwindEntities.Customers as c order by

c.CustomerID limit 10"

;

ObjectQuery

<

Customers

> query1 = edm.CreateQuery<

Customers

>(esql1);

string

esql2 =

"select value c from NorthwindEntities.Customers as c where

c.Country='UK' order by c.CustomerID limit 10"

;

ObjectQuery

<

Customers

> query2 = edm.CreateQuery<

Customers

>(esql2);

query1 = query1.Except(query2);