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LLBL Gen + Entity Framework 程序设计入门

2013-07-22 09:40 381 查看

Entity Framework推出有好几年，除了微软的Visual Studio可以做实体框架开发外，第三方的开发工具如LLBL Gen，

Devart Entity Developer也可以用来做设计开发。

设计数据库表Configuration，它的SQL定义如下

IF OBJECT_ID ('dbo.Configuration') IS NOT NULL
DROP TABLE dbo.Configuration
GO

CREATE TABLE dbo.Configuration
(
Recnum      INT IDENTITY NOT NULL,
MasterKey   NVARCHAR (50) NOT NULL,
Description TEXT NULL,
Remark      NVARCHAR (400) NULL,
CONSTRAINT PK_X_Config PRIMARY KEY (MasterKey)
)
GO

这里还有其它版本的Entity Framework。对应关系如下

Entity Framework v1 => Entity Framework 3.5 SP1

Entity Framework v4 => Entity Framework 4/4.5

再到Category Explorer窗口中，选择添加数据库映射，选择数据库类型，设置连接参数

生成实体模型，继续在Category Explorer窗口中，把表添加到当前项目的实体中，如下图所示

验证实体类型，准备生成代码，但是出现以下几个错误：

The Entity "FileType" contains field "FileType" which has the same name as its containing element,something which isn't supported by the Entity Framework

.csharpcode, .csharpcode pre
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.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
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width: 100%;
margin: 0em;
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.csharpcode .lnum { color: #606060; }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
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.csharpcode .lnum { color: #606060; }映射的实体名字段中，不能包含与实体名称一样的字段。比如，我有一个FileType的表，映射到FileType实体，它包含一个FileType的主键字段，自动生成映射时，这是不允许的。

清除这个错误之后，按F7生成代码，用Visual Studio 2012打开项目，如下图所示

LLBL Gen代码生成器帮忙我们生成Entity Framework所需要的edmx文件，类型定义和DataContext类型。

来看一下生成的类型定义代码，Configuration表映射的实体类型Configuration实体，它的代码如下

/// <summary>Class which represents the entity 'Configuration'.</summary>
[Serializable]
[DataContract(IsReference=true)]
[EdmEntityType(NamespaceName="Entity35Model", Name="Configuration")]
public partial class Configuration : CommonEntityBase
{
#region Class Member Declarations
private System.String _description;
private System.String _masterKey;
private System.Int32 _recnum;
private System.String _remark;
#endregion

#region Extensibility Method Definitions
partial void OnDescriptionChanging(System.String value);
partial void OnDescriptionChanged();
partial void OnMasterKeyChanging(System.String value);
partial void OnMasterKeyChanged();
partial void OnRecnumChanging(System.Int32 value);
partial void OnRecnumChanged();
partial void OnRemarkChanging(System.String value);
partial void OnRemarkChanged();
#endregion

/// <summary>Initializes a new instance of the <see cref="Configuration"/> class.</summary>
public Configuration() : base()
{
}

/// <summary>Factory method to create a new instance of the entity type 'Configuration'</summary>
/// <param name="masterKeyValue">The initial value for the field 'MasterKey'</param>
/// <param name="recnumValue">The initial value for the field 'Recnum'</param>
public static Configuration CreateConfiguration(System.String masterKeyValue, System.Int32 recnumValue)
{
var toReturn = new Configuration();
toReturn.MasterKey = masterKeyValue;
toReturn.Recnum = recnumValue;
return toReturn;
}

#region Class Property Declarations
/// <summary>Gets or sets the Description field. </summary>
[DataMember]
[EdmScalarProperty()]
public System.String Description
{
get    { return _description; }
set
{
OnDescriptionChanging(value);
this.ReportPropertyChanging("Description");
_description = SetValidValue(value, true);
this.ReportPropertyChanged("Description");
OnDescriptionChanged();
}
}

/// <summary>Gets or sets the MasterKey field. </summary>
[DataMember]
[EdmScalarProperty(EntityKeyProperty=true, IsNullable=false)]
public System.String MasterKey
{
get    { return _masterKey; }
set
{
if(_masterKey==value)
{
return;
}
OnMasterKeyChanging(value);
this.ReportPropertyChanging("MasterKey");
_masterKey = SetValidValue(value, false);
this.ReportPropertyChanged("MasterKey");
OnMasterKeyChanged();
}
}

/// <summary>Gets or sets the Recnum field. </summary>
[DataMember]
[EdmScalarProperty(IsNullable=false)]
public System.Int32 Recnum
{
get    { return _recnum; }
private set
{
OnRecnumChanging(value);
this.ReportPropertyChanging("Recnum");
_recnum = SetValidValue(value);
this.ReportPropertyChanged("Recnum");
OnRecnumChanged();
}
}

/// <summary>Gets or sets the Remark field. </summary>
[DataMember]
[EdmScalarProperty()]
public System.String Remark
{
get    { return _remark; }
set
{
OnRemarkChanging(value);
this.ReportPropertyChanging("Remark");
_remark = SetValidValue(value, true);
this.ReportPropertyChanged("Remark");
OnRemarkChanged();
}
}

#endregion
}

LLBL Gen让生成的实体类型派生于CommonEntityBase，这个类型派生于EntityObject，定义如下

/// <summary>Class which is the common base class for all generated entity classes.</summary>
/// <remarks>As all non-subtype entity classes derive from this class, use a partial class of this class to implement code which is shared among all generated entity classes</remarks>
[DataContract(IsReference = true)]
[Serializable]
public abstract partial class CommonEntityBase : EntityObject
{
#region Class Extensibility Methods
/// <summary>Method called from the constructor</summary>
partial void OnCreated();
#endregion

/// <summary>Initializes a new instance of the <see cref="CommonEntityBase"/> class.</summary>
protected CommonEntityBase() : base()
{
OnCreated();
}

}

可以在这个类型中，创建一些公共的方法以方便在生成的实体类型中使用。

LLBL Gen为实体框架的实体的每个属性添加了二个跟踪机制方法：Changing和Changed方法。这里可以写我们实体的业务逻辑。比如在采购单中，用户改变单价时，自动重新计算金额(金额=数量*单价)。

以备注属性为例子，请看下面的代码

/// <summary>Gets or sets the Remark field. </summary>
[DataMember]
[EdmScalarProperty()]
public System.String Remark
{
get    { return _remark; }
set
{
OnRemarkChanging(value);
this.ReportPropertyChanging("Remark");
_remark = SetValidValue(value, true);
this.ReportPropertyChanged("Remark");
OnRemarkChanged();
}
}

partial void OnRemarkChanging(System.String value);
partial void OnRemarkChanged();

这二个方法都是partial方法，如果我们没有定义方法体，则编译时，它会被忽略。partial方法是C# 3.0才引入的特性，为方便代码生成器与开发人员之间的合作更紧密。试想一下，怎么在不修改代码生成器生成的方法的情况下，添加自定义的业务代码到类型的方法，属性中去呢？答案是partial方法。

同时，因为生成的实体类型已经加了partial关键字，所以我们可以再加入一个同名的实体类型，用来写业务逻辑，而不更改代码生成器自动生成的代码。

最后，写一个测试方法，让它读取系统的配置表Configuration中的数据：

public static void Main(string[] args)
{
Entity35DataContext entity35DataContext = new Entity35DataContext();
var configurations = from item in entity35DataContext.Configurations
select item;

foreach (var dbDataRecord in configurations)
{
string companyCode = dbDataRecord.MasterKey;

}
}

一行代码即可完成数据库的读取，而且读取的数据是强类型，非常方便。

一般在入门例子中，容易出错的地方是配置文件的内容，来看一下App.config文件的内容：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings>
<!-- please adjust the connection string embedded in the element below to target the proper catalog / server using the proper user / password combination -->
<add name="ConnectionString.SQL Server (SqlClient)" connectionString="metadata=res://*/Entity35.csdl|res://*/Entity35.ssdl|res://*/Entity35.msl;provider=System.Data.SqlClient;provider connection string="data source=.\sqlexpress;initial catalog=Framework;integrated security=SSPI;persist security info=False;packet size=4096"" providerName="System.Data.EntityClient" />
</connectionStrings>
</configuration>

/// <summary>Initializes a new instance of the <see cref="Entity35DataContext"/> class using the connection string found in the 'Entity35' section of the application configuration file.</summary>
public Entity35DataContext() : base("name=ConnectionString.SQL Server (SqlClient)", "Entity35Entities")
{
Initialize();
}

/// <summary>Initializes a new instance of the <see cref="Entity35DataContext"/> class</summary>
public Entity35DataContext(string connectionString) : base(connectionString, "Entity35Entities")
{
Initialize();
}

/// <summary>Initializes a new instance of the <see cref="Entity35DataContext"/> class</summary>
/// <param name="connection">Ready to use EntityConnection object to be used with this context</param>
public Entity35DataContext(System.Data.EntityClient.EntityConnection connection) : base(connection, "Entity35Entities")
{
Initialize();
}

Entity Framework的连接字符串与经常写的SQL Server的SqlConnection的字符串有所区别，要指定依据edmx生成的三个文件的位置，因为edmx文件的Build Action为EntityDeploy，所以它会被嵌入到生成的程序集中。

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background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

用.NET Reflector载入生成的实体程序集，查看它的资源文件，如上图所示，三个资源文件被嵌入在程序集中。

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background-color: #ffffff;
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.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

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