Entity Framework之查询总结 / 憋错料

本节针对EF当前支持的查询方式进行分析比较，和简单自定义条件查询的实现。

EF的查询方式
自定义条件查询

一、EF的查询方式

EF提供的查询方式有以下几种

原始SQL查询
LINQ To Entity and Lambda
ESQL 与 ObjectQuery
ObjectQuery 查询生成器

1.原始SQL查询

在EF 4.1 新增加的DbContext 除了支持LINQ与Lambda查询外，新增了支持原始SQL查询，但是不支持ESQL与ObjectQuery查询。

DemoDBEntities context = new DemoDBEntities();

DbSet
<
BlogMaster
>

set

=
context.Set
<
BlogMaster
>
();

List
<
BlogMaster
>
list
=

set
.SqlQuery(
"
select *from BlogMaster where UserId=‘3‘
"
).ToList();

List
<
BlogMaster
>
listAll
=
context.Database.SqlQuery
<
BlogMaster
>
(
"
select *from BlogMaster
"
).ToList();

使用原始SQL查询，既灵活又方便维护，加上DbContext泛型处理，可以将最终的查询数据集映射成对象集合。而且SQL语句有错误时，提醒也比较明确。项目中，大家都会碰到查询条件经常变动的问题，针对这种情况我们以使用通过定制的查询模板以SQL拼接的方式解决，而不是修改代码。

2.LINQ To Entity and Lambda

这两种是比较常用的方式，也是效率比较高的，简洁方便，但是不灵活，如果条件变了，可能就需要修改代码。相信做过报表的人都曾为复杂的SQL语句以及SQL语句的执行效率头痛过，而LINQ和Lambda 方便就在于可以将复杂的SQL拆分出来，在内存中解决这些数据的合并筛选，并且效率要远高于SQL。我最喜欢的LINQ的一个功能就是他的分组。

DemoDBEntities context
=

new
DemoDBEntities();

DbSet
<
BlogMaster
>

set

=
context.Set
<
BlogMaster
>
();

var result
=
from u
in

set
.ToList()

where
u.UserID
==

select u;

var resultGroup
=
from u
in

set
.ToList()
group u by u.UserID
into g
select g;

var list
=

set
.Where(o
=>
o.UserID
==

3
);
var listGroup
=

set
.GroupBy(o
=>
o.UserID);

不管是哪种方式，LINQ To Entity and Lambda EF 都是支持的。

3.ESQL 与 ObjectQuery

首先说明一点，目前DbContext不支持这种方式查询。ESQL同原始SQL 只是写法稍为有点区别，但是特点差不多，灵活易于维护。由于可以拼接ESQL，所以这种方式也可以应对查询条件变化。

DemoDBEntities context
=

new
DemoDBEntities();

//
DbSet<BlogMaster> set = context.Set<BlogMaster>();

string
queryString
=

@"
SELECT VALUE it FROM DemoDBEntities.BlogMaster as
it WHERE it.UserId > @UserId order by it.UserId desc
"
;
ObjectQuery
<
BlogMaster
>
query
=

new
ObjectQuery
<
BlogMaster
>
(queryString, context);

//
Add parameters to the collection.

query.Parameters.Add(
new
ObjectParameter(
"
UserId
"
,
6
));

List
<
BlogMaster
>
list
=
query.ToList();

原始SQL与ESQL 区别在于参数类型的处理，因为原始的SQL你在拼接的条件的时候要对不同的参数值类型处理，例如是where Name=‘tt‘ and UserId=6 and Sex=true ，而ESQL则是object传入，直接实现SQL语句的转换。可惜DbContext不支持ESQL，所以只能自己去解决SQL条件不同值类型的拼接处理。

4.ObjectQuery 查询生成器

DemoDBEntities context
=

new
DemoDBEntities();

ObjectQuery
<
BlogMaster
>
query
=
context.CreateObjectSet
<
BlogMaster
>
()
.Where(
"
it.UserId > @UserId
"
,

new
ObjectParameter(
"
UserId
"
,
6
))
.OrderBy(
"
it.UserId desc
"
);

List
<
BlogMaster
>
list
=
query.ToList();

这种方式基本上有ESQL相同，只是分组，排序，条件过滤都要单独处理，相比就没结合ESQL使用灵活了。

以上四种方式各有优缺点，如果是批量做页面的查询，每个查询页面和条件各不相同，并且查询条件可能会变动的话，建议使用DbContext的SQL查询，或者是ESQL结合ObjectQuery，这两种方式易于通过查询模板拼接生成SQL语句，但不适合生成复杂的SQL语句。而LINQ or Lambda 以及ObjectQuery方式，则不适合做一些重复查询逻辑的工作，而单独处理一些页面的查询或者复杂的报表还是比较灵活的。

二、自定义条件查询

基于自定义条件查询，不适合处理过于复杂的条件查询语句。我们来看一下思路

假如WEB前台或是应用界面有一些查询字段，A需要Like ,B是=，C是> 某个时间并<小于某个时间，以后可能会增加D，或E。为了不修改代码，而仅仅拖拉控件设置属性就可新增查询条件，下面以WINFORM为例，WEB类似操作（你可以将查询条件以XML或JSON形式传回后台）。

首先对Winform几个控件进行扩展处理，首先设计个扩展接口IExtControl，IExtControl 有以下几个属性

ExtUsingType 控件使用类型用于控制是否可编辑

ExtDataField 指向数据库的查询字段

ExtDataValue 查询字段值

ExtQueryExpression 查询表达式是like ?= ? >?

我们对TextBox，CheckBox，ComBox，DateTimePicker 进行扩展代码如下

using
System;

using
System.Collections.Generic;

using
System.Linq;

using
System.Text;

using
System.Windows.Forms;

using
System.ComponentModel;

namespace
FinancialSystem
{

public

interface
IExtControl
{

///

///
使用类型

///

</summary>

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
控件使用类型
"
)]
ExtUsingTypeEnum ExtUsingType
{

set
;

get
;
}

///

///
数据字段名称

///

</summary>

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
指向数据库表某个字段
"
)]

string
ExtDataField
{

set
;

get
;
}

///

///
数据字段名称

///

</summary>

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
指向数据库表字段对应的值
"
)]

string
ExtDataValue {
set
;
get
; }

///

///
查询表达式

///

</summary>

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
查询表达式选择
"
)]
ExtQueryExpressionEnum ExtQueryExpression {
get
;
set
; }

///

///
清空值

///

</summary>

void
ClearDataValue();
}

public

class
ExtTextBox : TextBox, IExtControl
{

#region
IExtControl 成员

private
ExtUsingTypeEnum extUsingType
=
ExtUsingTypeEnum.Query;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
控件使用类型
"
)]

public
ExtUsingTypeEnum ExtUsingType
{

get

{

return
extUsingType;
}

set

{
extUsingType
=
value;
}
}

private

string
extDataField;

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
指向数据库表某个字段
"
)]

public

string
ExtDataField
{

get

{

return
extDataField;
}

set

{
extDataField
=
value;
}
}

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
字段值
"
)]

public

string
ExtDataValue
{

get
{
return

this
.Text.ToString(); }

set
{
this
.Text
=
value; }
}

private
ExtQueryExpressionEnum extQueryExpression
=
ExtQueryExpressionEnum.EQ;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
查询表达式选择
"
)]

public
ExtQueryExpressionEnum ExtQueryExpression
{

get

{

return
extQueryExpression;
}

set

{
extQueryExpression
=
value;
}
}

public

void
ClearDataValue()
{

this
.Text
=

""
;
}

#endregion

}

public

class
ExtComBox : ComboBox, IExtControl
{

#region
IExtControl 成员

private
ExtUsingTypeEnum extUsingType
=
ExtUsingTypeEnum.Query;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
控件使用类型
"
)]

public
ExtUsingTypeEnum ExtUsingType
{

get

{

return
extUsingType;
}

set

{
extUsingType
=
value;
}
}

private

string
extDataField;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
指向数据库表某个字段
"
)]

public

string
ExtDataField
{

get

{

return
extDataField;
}

set

{
extDataField
=
value;
}
}

private
ExtQueryExpressionEnum extQueryExpression
=
ExtQueryExpressionEnum.EQ;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
查询表达式选择
"
)]

public
ExtQueryExpressionEnum ExtQueryExpression
{

get

{

return
extQueryExpression;
}

set

{
extQueryExpression
=
value;
}
}

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
字段值
"
)]

public

string
ExtDataValue
{

get
{
return

this
.SelectedValue
==
null
?
""
:
this
.SelectedValue.ToString(); }

set
{
this
.SelectedValue
=
value; }
}

///

///
清空值

///

</summary>

public

void
ClearDataValue()
{

this
.SelectedValue
=

-
1
;
}

#endregion

}

public

class
ExtCheckBox : CheckBox, IExtControl
{

#region
IExtControl 成员

private
ExtUsingTypeEnum extUsingType
=
ExtUsingTypeEnum.Query;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
控件使用类型
"
)]

public
ExtUsingTypeEnum ExtUsingType
{

get

{

return
extUsingType;
}

set

{
extUsingType
=
value;
}
}

private

string
extDataField;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
指向数据库表某个字段
"
)]

public

string
ExtDataField
{

get

{

return
extDataField;
}

set

{
extDataField
=
value;
}
}

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
字段值
"
)]

public

string
ExtDataValue
{

get

{

if
(
this
.Checked)

return

"
True
"
;

else

return

"
False
"
;
}

set

{

if
(value
==

"
True
"
)

this
.Checked
=

true
;

else

this
.Checked
=

false
;
}
}

private
ExtQueryExpressionEnum extQueryExpression
=
ExtQueryExpressionEnum.EQ;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
查询表达式选择
"
)]

public
ExtQueryExpressionEnum ExtQueryExpression
{

get

{

return
extQueryExpression;
}

set

{
extQueryExpression
=
value;
}
}

///

///
清空值

///

</summary>

public

void
ClearDataValue()
{

this
.Checked
=

false
;
}

#endregion

}

public

class
ExtDateTimePicker : DateTimePicker, IExtControl
{

#region
IExtControl 成员

private
ExtUsingTypeEnum extUsingType
=
ExtUsingTypeEnum.Edit;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
控件使用类型
"
)]

public
ExtUsingTypeEnum ExtUsingType
{

get

{

return
extUsingType;
}

set

{
extUsingType
=
value;
}
}

private

string
extDataField;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
指向数据库表某个字段
"
)]

public

string
ExtDataField
{

get

{

return
extDataField;
}

set

{
extDataField
=
value;
}
}

[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
字段值
"
)]

public

string
ExtDataValue
{

get
{
return

this
.Value.ToString(); }

set
{
this
.Text
=
value; }
}

private
ExtQueryExpressionEnum extQueryExpression
=
ExtQueryExpressionEnum.EQ;
[Category(
"
Ext-扩展属性
"
)]
[Browsable(
true
)]
[Description(
"
查询表达式选择
"
)]

public
ExtQueryExpressionEnum ExtQueryExpression
{

get

{

return
extQueryExpression;
}

set

{
extQueryExpression
=
value;
}
}

///

///
清空值

///

</summary>

public

void
ClearDataValue()
{

this
.Value
=
DateTime.Now;
}

#endregion

}

public

class
ExtDataGridViewTextBoxColumn : DataGridViewTextBoxColumn, IExtControl
{

#region
IExtControl 成员

public
ExtUsingTypeEnum ExtUsingType
{

get

{

throw

new
NotImplementedException();
}

set

{

throw

new
NotImplementedException();
}
}

public

string
ExtDataField
{

get

{

throw

new
NotImplementedException();
}

set

{

throw

new
NotImplementedException();
}
}

public

string
ExtDataValue
{

get

{

throw

new
NotImplementedException();
}

set

{

throw

new
NotImplementedException();
}
}

public
ExtQueryExpressionEnum ExtQueryExpression
{

get

{

throw

new
NotImplementedException();
}

set

{

throw

new
NotImplementedException();
}
}

public

void
ClearDataValue()
{

throw

new
NotImplementedException();
}

#endregion

}
}

查询表达式枚举

using
System;

using
System.Collections.Generic;

using
System.Linq;

using
System.Text;

namespace
FinancialSystem
{

public

enum
ExtUsingTypeEnum
{
Query
=

0
,
Edit
=

1
,
Normal
=

}

public

enum
ExtQueryExpressionEnum
{
LK
=

0
,
EQ
=

1
,
IN
=

2
,
YEARANDMONTH
=

3
,
FR
=

4
,
TO
=

5
,
UE
=

6
,
GT
=

7
,
LT
=

8
,
NOTNULL
=
9
,
ISNULL
=
10
,
OR
=
11
,
SK
=
8

}
}

完成上面工作后，我们VS左侧工具栏就可以看到我们新扩展的控件

我们利用上面的扩展控件设计个查询界面，右键控件属性，分别设置ExtDataField,ExtQueryExpression值

设置控件属性，新增查询控件就直接拖到界面上，设置对应数据库查询字段及查询方式即可

上面我们就完成了自定义查询的界面的设计，接下来就是读取这些控件的扩展属性生成SQL查询条件，代码如下

using
System;

using
System.Collections.Generic;

using
System.Linq;

using
System.Text;

using
System.Windows.Forms;

using
System.Data;

using
System.IO;

namespace
EF.WinForm
{

public

class
QueryHelper
{

///

///
清空查询条件

///

</summary>

///

public

static

void
ClearWhereString(Control parentControl)
{

if
(parentControl
==

null
)

throw

new
ArgumentNullException(
"
装载查询控件的容器不存在!
"
);

foreach
(Control control
in
parentControl.Controls)
{

if
(control
is
IExtControl)
{

if
(control.Enabled)
{
IExtControl extControl
=
(IExtControl)control;
extControl.ClearDataValue();
}
}
}
}

///

///
读取生成查询条件

///

</summary>

///

///

public

static

string
GetWhereString(Control parentControl)
{

return
GetWhereString(parentControl,
"
And
"
);

}

///

///
读取查询条件(web直接处理传回的XML，或者JSON字符串)

///

</summary>

///

///

///

public

static

string
GetWhereString(Control parentControl,
string
logic)
{

if
(parentControl
==

null
)

throw

new
ArgumentNullException(
"
装载查询控件的容器不存在!
"
);

string
whereStr
=
""
;

foreach
(Control control
in
parentControl.Controls)
{

if
(control
is
IExtControl)
{
IExtControl extControl
=
(IExtControl)control;

if
(extControl.ExtDataValue.Trim()
!=
""
)
whereStr
+=

"
(
"
+
GetMatch(extControl.ExtDataField,extControl.ExtQueryExpression.ToString(),extControl.ExtDataValue)
+
"
)
"
+
logic;
}

}

if
(whereStr
==

""
)

return

""
;

else

return

"
where
"

+
whereStr.Substring(
0
, whereStr.Length
-
logic.Length);

}

///

///
根据匹配域，匹配方法，匹配域值取得匹配条件串

///

</summary>

///

<param name="fieldName">
匹配域名称(同数据库一致)
</param>

///

///

<param name="fieldValue">
匹配域的值
</param>

///

<returns>
域的条件串
</returns>

public

static

string
GetMatch(
string
fieldName,
string
match,
string
fieldValue)
{

string
mop
=
"
=
"
;
fieldValue
=
fieldValue.Replace(
"
‘
"
,
"
‘‘
"
);

if
(AttrIsNull(match))
match
=

"
EQ
"
;

switch
(match.ToUpper())
{

case

"
EQ
"
:
mop
=
fieldName
+

"
=‘
"

+
fieldValue
+

"
‘
"
;

break
;

case

"
UE
"
:
mop
=
fieldName
+

"
<>‘
"

+
fieldValue
+

"
‘
"
;

break
;

case

"
GT
"
:
mop
=
fieldName
+

"
>‘
"

+
fieldValue
+

"
‘
"
;

break
;

case

"
LT
"
:
mop
=
fieldName
+

"
<‘
"

+
fieldValue
+

"
‘
"
;

break
;

case

"
IN
"
:

string
[] flds
=
fieldValue.Split(
‘
,
‘
);

string
fldstr
=
""
;

for
(
int
i
=
0
;i
<
flds.Length;i
++
)
fldstr
+=
"
‘
"
+
flds[i]
+
"
‘,
"
;
fldstr
=
fldstr.Substring(
0
,fldstr.Length
-
1
);
mop
=
fieldName
+

"
IN (
"

+
fldstr
+

"
)
"
;

break
;

case

"
FR
"
:
mop
=
fieldName
+

"
>=‘
"

+
fieldValue
+

"
‘
"
;

break
;

case

"
TO
"
:
mop
=
fieldName
+

"
<=‘
"

+
fieldValue
+

"
‘
"
;

break
;

case

"
LK
"
:
mop
=
fieldName
+

"
LIKE ‘%
"

+
fieldValue
+

"
%‘
"
;

break
;

case

"
SK
"
:

string
[] flds0
=
fieldValue.Split(
‘

‘
);

string
fldstr0
=
"
%
"
;

for
(
int
i
=
0
;i
<
flds0.Length;i
++
)

if
(flds0[i].Trim()
!=
""
)
fldstr0
+=
flds0[i]
+
"
%
"
;
mop
=
fieldName
+

"
LIKE ‘
"

+
fldstr0
+

"
‘
"
;

break
;

case

"
NOTNULL
"
:
mop
=
fieldName
+

"
IS NOT NULL and
"
+
fieldName
+

"
<>‘‘
"
;

break
;

case

"
ISNULL
"
:
mop
=
fieldName
+

"
IS NULL or
"
+
fieldName
+

"
=‘‘
"
;

break
;

case

"
OR
"
:

string
[] flds1
=
fieldValue.Split(
‘

‘
);

string
fldstr1
=
""
;

for
(
int
i
=
0
;i
<
flds1.Length;i
++
)

if
(flds1[i].Trim()
!=
""
)
fldstr1
+=
fieldName
+

"
Like ‘%
"
+
flds1[i]
+
"
%‘ or
"
;
fldstr1
=
fldstr1.Substring(
0
,fldstr1.Length
-
3
);
mop
=
"
(
"

+
fldstr1
+

"
)
"
;

break
;

case

"
YEARANDMONTH
"
:
mop
=

string
.Format(
"
YEAR({0})=YEAR(‘{1}‘) and MONTH({0})=MONTH(‘{1}‘)
"
, fieldName, fieldValue);

break
;
}

return
mop;
}

public

static

bool
AttrIsNull(
string
attr)
{
if
(attr
==

null

||
attr
==

""
)

return

true
;

else

return

false
;
}

}
}

这段代码的基本业务就是查找所有继随IExtControl的接口控件，读取其中的字段，值，及查询方式拼接生成SQL where条件

继续来调用QueryHelper实现Winform的查询代码

using
System;

using
System.Collections.Generic;

using
System.ComponentModel;

using
System.Data;

using
System.Drawing;

using
System.Linq;

using
System.Text;

using
System.Windows.Forms;

using
EF.Model;

using
EF.BLL;

namespace
EF.WinForm
{

public

partial

class
FrmMain : Form
{

public
FrmMain()
{
InitializeComponent();
}

private

void
btnQuery_Click(
object
sender, EventArgs e)
{

//
获取自定义查询条件

string
whereStr
=
QueryHelper.GetWhereString(
this
.groupBox1);

//
读取数据（BLL层调用DAL层的context SqlQuery方法实现

BlogArticleService service
=
new
BlogArticleService();
List
<
BlogArticle
>
list
=
service.SqlQuery(whereStr,
""
);

this
.bindingSource.DataSource
=
list;

this
.bindingNavigator.BindingSource
=
bindingSource;

this
.dataGridView.DataSource
=

this
.bindingSource;
}

private

void
btnClear_Click(
object
sender, EventArgs e)
{
QueryHelper.ClearWhereString(
this
.groupBox2);
}

private

void
FrmMain_Load(
object
sender, EventArgs e)
{
BlogCategoryService service
=

new
BlogCategoryService();
List
<
BlogCategory
>
list
=
service.FindAll();

this
.extComBox1.DataSource
=
list;

this
.extComBox1.DisplayMember
=

"
CateName
"
;

this
.extComBox1.ValueMember
=

"
CateID
"
;
}
}
}

运行后查看结果

如果再新增查询条件，我们只要拖个控制设置一下对应数据库属性，这样不用修改后台代码了。例如：

以上就是EF 基于原始SQL实现的简易自定义查询功能，不是很完善。我们可以再继续封装排序，分页等查询功能。

using
System;

using
System.Collections.Generic;

using
System.Linq;

using
System.Text;

using
EF.DAL;

using
EF.Model;

namespace
EF.BLL
{

public

class
BlogArticleService
{
IRepository
<
BlogArticle
>
repository;

public
BlogArticleService(IRepository
<
BlogArticle
>
repository)
{

this
.repository
=
repository;
}

public
BlogArticleService()
{

this
.repository
=

new
BlogArticleRepository();
}

public
BlogArticle Create()
{

return
repository.Create();
}

public
BlogArticle Insert(BlogArticle entity)
{

return
repository.Insert(entity);
}

public
BlogArticle Update(BlogArticle entity)
{

return
repository.Update(entity);
}

public

void
Delete(BlogArticle entity)
{
repository.Delete(entity);
}

//
为了演示，查询可单独提取一个接口类同Resposity用法相同

public
List
<
BlogArticle
>
SqlQuery(
string
sqlString)
{

return
repository.SqlQuery(sqlString);
}

//
为了演示，查询可单独提取一个接口类同Resposity用法相同

public
List
<
BlogArticle
>
SqlQuery(
string
whereStr,
string
orderStr)
{

string
tableName
=

typeof
(BlogArticle).Name;

string
sqlString
=

string
.Format(
"
select *from {0} {1} {2}
"
, tableName, whereStr, orderStr);

return
repository.SqlQuery(sqlString);
}

//
实现一个简易分页功能

public
List
<
BlogArticle
>
SqlQuery(
string
whereStr,
string
orderStr,
ref

int
pageIndex,
ref

int
pageCount,
ref

int
sumCount)
{

string
tableName
=

typeof
(BlogArticle).Name;

string
sqlString
=

string
.Format(
"
select *from {0} {1} {2}
"
, tableName, whereStr, orderStr);
List
<
BlogArticle
>
list
=
repository.SqlQuery(sqlString);
sumCount
=
list.Count;

return
list.Skip(pageIndex).Take(pageCount).ToList();
}

//
为了演示，查询可单独提取一个接口类同Resposity用法相同

public
List
<
BlogArticle
>
SqlQuery(
string
fields,
string
whereStr,
string
orderStr)
{

string
tableName
=

typeof
(BlogArticle).ToString();

string
sqlString
=

string
.Format(
"
select {0} from {1} {2} {3}
"
, fields, tableName, whereStr, orderStr);

return
repository.SqlQuery(sqlString);
}

}
}

利用ESQL结合ObjectQuery同样实现这个功能，并且不用处理值类型转换。如果DbContext 在后面支持了ESQL，建议还是用ESQL 处理。

源码下载

参考页面：