LLBL Gen + Entity Framework 程序设计入门

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

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打开LLBL Gen，创建一个新项目，选择Entity Framework v1

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

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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();
            }
}

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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=&quot;data source=.\sqlexpress;initial catalog=Framework;integrated security=SSPI;persist security info=False;packet size=4096&quot;" providerName="System.Data.EntityClient" />
    </connectionStrings>
</configuration> 

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.csharpcode .lnum { color: #606060; }这里是设置连接字符串的地方，从生成的ObjectContext类型中，可以看到不带参数的构造方法为从这里读取连接字符串，它的其它的几个方法，如下代码所示

/// <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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.csharpcode .asp { background-color: #ffff00; }
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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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