如何为 EF4 实体上的属性提取数据库表和列名？

Question

我正在为使用 EF4 作为数据访问层的应用程序编写审核组件。我能够很容易地确定哪些实体已被修改，并且通过 ObjectStateEntry 对象我可以提取原始值、当前值、实体名称和已修改的属性名称，但我还想提取原始表和SQL Server 中使用的列名（因为它们并不总是与模型的实体和属性名称匹配）

有谁知道这样做的好方法吗？甚至可能吗？映射显然存储在 MSL 中，但我无法找到以编程方式访问这些映射的方法。

Answer 1

查看实体框架模型设计器后，我看到它使用EdmEntityTypeAttribute 和DataMemberAttribute 来装饰生成的类和属性。它们每个都有一个Name 属性，其中包含映射实体的名称（分别为表、列）。当属性名称与列名称匹配时，设计器不会为位置参数Name 提供值。 下面的代码对我来说很好。

 private static string GetTableName<T>() where T : EntityObject
    {
        Type type = typeof(T);
        var at = GetAttribute<EdmEntityTypeAttribute>(type);
        return at.Name;
    }

    private static string GetColumnName<T>(Expression<Func<T, object>> propertySelector) where T : EntityObject
    {
        Contract.Requires(propertySelector != null, "propertySelector is null.");

        PropertyInfo propertyInfo = GetPropertyInfo(propertySelector.Body);
        DataMemberAttribute attribute = GetAttribute<DataMemberAttribute>(propertyInfo);
        if (String.IsNullOrEmpty(attribute.Name))
        {
            return propertyInfo.Name;
        }
        return attribute.Name;
    }

    private static T GetAttribute<T>(MemberInfo memberInfo) where T : class
    {
        Contract.Requires(memberInfo != null, "memberInfo is null.");
        Contract.Ensures(Contract.Result<T>() != null);

        object[] customAttributes = memberInfo.GetCustomAttributes(typeof(T), false);
        T attribute = customAttributes.Where(a => a is T).First() as T;
        return attribute;
    }

    private static PropertyInfo GetPropertyInfo(Expression propertySelector)
    {
        Contract.Requires(propertySelector != null, "propertySelector is null.");
        MemberExpression memberExpression = propertySelector as MemberExpression;
        if (memberExpression == null)
        {
            UnaryExpression unaryExpression = propertySelector as UnaryExpression;
            if (unaryExpression != null && unaryExpression.NodeType == ExpressionType.Convert)
            {
                memberExpression = unaryExpression.Operand as MemberExpression;
            }
        }
        if (memberExpression != null && memberExpression.Member.MemberType == MemberTypes.Property)
        {
            return memberExpression.Member as PropertyInfo;
        }
        throw new ArgumentException("No property reference was found.", "propertySelector");
    }

    // Invocation example
    private static Test()
    {
         string table = GetTableName<User>();
         string column = GetColumnName<User>(u=>u.Name);
    }

Answer 2

所有的模型数据都可以通过这个方法获得 myObjectContext.MetadataWorkspace.GetEntityContainer(myObjectContext.DefaultContainerName, DataSpace.CSSpace);

这至少应该让你开始了解如何做你想做的事。 DataSpace.CSSpace 指定概念名称和商店名称之间的映射。 DataSpace.CSpace 为您提供概念模型，DataSpace.SSpace 为您提供存储模型。

Answer 3

如果您编写代码来审核映射，您不是真的在审核/验证 Microsoft 的 EF 代码吗？也许这可以安全地定义在问题域之外，除非审计的目的是建立对 EF 本身的信心。

但是，如果您确实需要进行此类审核，一种可能性可能是添加构建步骤以将 .edmx 文件作为资源嵌入您正在检查的 DLL 中。你没有说你是否在被测 DLL 上有这种控制/输入。不过，这将是一个 hack —— 正如 JasCav 所说，ORM 的目的是让你尝试的东西变得不必要。

Answer 4

这是一个在概念信息和商店信息之间转换的通用算法，用 Visual Basic 2010 编写。

我编写了一个新例程，将实体/属性对转换为表/列对。此类 MSLMappingAction 在其构造函数中接受模型名称和 XElement XML 树、MSL 映射文件或 XML 字符串。然后使用 ConceptualToStore 方法获取 String 指定实体和属性“表达式”（存储在 MSLConceptualInfo 结构中）并找到表和列名称（存储在 MSLStoreInfo 结构）。

注意事项：

1. 也可以编写一个“StoreToConceptual”方法来转换 另一个方向，但 XML 查询可能会有点 更复杂。处理也是如此 导航属性/功能/存储过程映射。
2. 注意派生实体的继承属性！ 如果一个属性是 不特定于派生实体，那么您应该使用基础 实体名称。）

这是代码。

主机代码：（对于给出的 XML 示例 [见底部]，当给定实体“Location”和属性表达式“Address.Street”[和概念模型名称“SCTModel”]）：

Dim MSL As MSLMappingAction = New MSLMappingAction(".\SCTModel.msl", "SCTModel")

Dim ConceptualInfo As MSLConceptualInfo = New MSLConceptualInfo With {.EntityName = "Location", .PropertyName = "Address.Street"}
Dim StoreInfo As MSLStoreInfo = MSL.ConceptualToStore(ConceptualInfo)
MessageBox.Show(StoreInfo.TableName & ": " & StoreInfo.ColumnName)

类代码：

Option Infer On
Imports System.Xml.Linq

''' <summary>
''' This class allows one to convert between an EF conceptual model's entity/property pair
''' and its database store's table/column pair.
''' </summary>
''' <remarks>It takes into account entity splitting and complex-property designations;
''' it DOES NOT take into account inherited properties
''' (in such a case, you should access the entity's base class)</remarks>
Public Class MSLMappingAction

'   private fields and routines
Private mmaMSLMapping As XElement
Private mmaModelName, mmaNamespace As String

Private Function FullElementName(ByVal ElementName As String) As String
'   pre-pend Namespace to ElementName
Return "{" & mmaNamespace & "}" & ElementName
End Function

Private Sub ValidateParams(ByVal MappingXML As XElement, Byval ModelName As String)
'   verify that model name is specified
If String.IsNullOrEmpty(ModelName) Then
    Throw New EntityException("Entity model name is not given!")
End If
'   verify that we're using C-S space
If MappingXML.@Space <> "C-S" Then
    Throw New MetadataException("XML is not C-S mapping data!")
End If
'   get Namespace and set private variables
mmaNamespace = MappingXML.@xmlns
mmaMSLMapping = MappingXML : mmaModelName = ModelName
End Sub

Private Function IsSequenceEmpty(Items As IEnumerable(Of XElement)) As Boolean
'   determine if query result is empty
Return _
    Items Is Nothing OrElse Items.Count = 0
End Function

'   properties
''' <summary>
''' Name of conceptual entity model
''' </summary>
''' <returns>Conceptual-model String</returns>
''' <remarks>Model name can only be set in constructor</remarks>
Public ReadOnly Property EntityModelName() As String
Get
    Return mmaModelName
End Get
End Property

''' <summary>
''' Name of mapping namespace
''' </summary>
''' <returns>Namespace String of C-S mapping layer</returns>
''' <remarks>This value is determined when the XML mapping
''' is first parsed in the constructor</remarks>
Public ReadOnly Property MappingNamespace() As String
Get
    Return mmaNamespace
End Get
End Property

'   constructors
''' <summary>
''' Get C-S mapping information for an entity model (with XML tree)
''' </summary>
''' <param name="MappingXML">XML mapping tree</param>
''' <param name="ModelName">Conceptual-model name</param>
''' <remarks></remarks>
Public Sub New(ByVal MappingXML As XElement, ByVal ModelName As String)
ValidateParams(MappingXML, ModelName)
End Sub

''' <summary>
''' Get C-S mapping information for an entity model (with XML file)
''' </summary>
''' <param name="MSLFile">MSL mapping file</param>
''' <param name="ModelName">Conceptual-model name</param>
''' <remarks></remarks>
Public Sub New(ByVal MSLFile As String, ByVal ModelName As String)
Dim MappingXML As XElement = XElement.Load(MSLFile)
ValidateParams(MappingXML, ModelName)
End Sub

'   methods
''' <summary>
''' Get C-S mapping infomration for an entity model (with XML String)
''' </summary>
''' <param name="XMLString">XML mapping String</param>
''' <param name="ModelName">Conceptual-model name</param>
''' <returns></returns>
Public Shared Function Parse(ByVal XMLString As String, ByVal ModelName As String)
Return New MSLMappingAction(XElement.Parse(XMLString), ModelName)
End Function

''' <summary>
''' Convert conceptual entity/property information into store table/column information
''' </summary>
''' <param name="ConceptualInfo">Conceptual-model data
''' (.EntityName = entity expression String, .PropertyName = property expression String)</param>
''' <returns>Store data (.TableName = table-name String, .ColumnName = column-name String)</returns>
''' <remarks></remarks>
Public Function ConceptualToStore(ByVal ConceptualInfo As MSLConceptualInfo) As MSLStoreInfo
Dim StoreInfo As New MSLStoreInfo
With ConceptualInfo
    '   prepare to query XML
    If Not .EntityName.Contains(".") Then
        '   make sure entity name is fully qualified
        .EntityName = mmaModelName & "." & .EntityName
    End If
    '   separate property names if there's complex-type nesting
    Dim Properties() As String = .PropertyName.Split(".")
    '   get relevant entity mapping
    Dim MappingInfo As IEnumerable(Of XElement) = _                 
        (From mi In mmaMSLMapping.Descendants(FullElementName("EntityTypeMapping")) _
            Where mi.@TypeName = "IsTypeOf(" & .EntityName & ")" _
                OrElse mi.@TypeName = .EntityName _
         Select mi)
    '   make sure entity is in model
    If IsSequenceEmpty(MappingInfo) Then
        Throw New EntityException("Entity """ & .EntityName & """ was not found!")
    End If
    '   get mapping fragments
    Dim MappingFragments As IEnumerable(Of XElement) = _
        (From mf In MappingInfo.Descendants(FullElementName("MappingFragment")) _
         Select mf)
    '   make sure there's at least 1 fragment
    If IsSequenceEmpty(MappingFragments) Then
        Throw New EntityException("Entity """ & .EntityName & """ was not mapped!")
    End If
    '   search each mapping fragment for the desired property
    For Each MappingFragment In MappingFragments
        '   get physical table for this fragment
        StoreInfo.TableName = MappingFragment.@StoreEntitySet
        '   search property expression chain
        Dim PropertyMapping As IEnumerable(Of XElement) = {MappingFragment}
        '   parse complex property info (if any)
        For index = 0 To UBound(Properties) - 1
            '   go down 1 level
            Dim ComplexPropertyName = Properties(index)
            PropertyMapping = _
                (From pm In PropertyMapping.Elements(FullElementName("ComplexProperty")) _
                    Where pm.@Name = ComplexPropertyName)
            '   verify that the property specified for this level exists
            If IsSequenceEmpty(PropertyMapping) Then
                Exit For 'go to next fragment if not
            End If
        Next index
        '   property not found? try next fragment
        If IsSequenceEmpty(PropertyMapping) Then
            Continue For
        End If
        '   parse scalar property info
        Dim ScalarPropertyName = Properties(UBound(Properties))
        Dim ColumnName As String = _
            (From pm In PropertyMapping.Elements(FullElementName("ScalarProperty")) _
                Where pm.@Name = ScalarPropertyName _
                Select CN = pm.@ColumnName).FirstOrDefault
        '   verify that scalar property exists
        If Not String.IsNullOrEmpty(ColumnName) Then
            '   yes? return (exit) with column info
            StoreInfo.ColumnName = ColumnName : Return StoreInfo
        End If
    Next MappingFragment
    '   property wasn't found
    Throw New EntityException("Property """ & .PropertyName _
        & """ of entity """ & .EntityName & """ was not found!")
End With
End Function
End Class

''' <summary>
''' Conceptual-model entity and property information  
''' </summary>
Public Structure MSLConceptualInfo
''' <summary>
''' Name of entity in conceptual model
''' </summary>
''' <value>Entity expression String</value>
''' <remarks>EntityName may or may not be fully qualified (i.e., "ModelName.EntityName");
''' when a mapping method is called by the MSLMappingAction class, the conceptual model's
''' name and a period will be pre-pended if it's omitted</remarks>
Public Property EntityName As String
''' <summary>
''' Name of property in entity
''' </summary>
''' <value>Property expression String</value>
''' <remarks>PropertyName may be either a stand-alone scalar property or a scalar property
''' within 1 or more levels of complex-type properties; in the latter case, it MUST be fully
''' qualified (i.e., "ComplexPropertyName.InnerComplexPropertyName.ScalarPropertyName")</remarks>
Public Property PropertyName As String
End Structure

''' <summary>
''' Database-store table and column information
''' </summary>
Public Structure MSLStoreInfo
''' <summary>
''' Name of table in database
''' </summary>
Public Property TableName As String
''' <summary>
''' Name of column in database table
''' </summary>
Public Property ColumnName As String
End Structure

关键是节点名称都必须有一个命名空间。它把我绊倒了，直到我一次检查我的元素 1！

这是示例 XML——我从上面代码中的“.\SCTModel.msl”文件加载：

<?xml version="1.0" encoding="utf-8"?>
<Mapping Space="C-S" xmlns="http://schemas.microsoft.com/ado/2008/09/mapping/cs">
  <EntityContainerMapping StorageEntityContainer="SCTModelStoreContainer" CdmEntityContainer="SocialContactsTracker">
    <EntitySetMapping Name="SocialContacts">
      <EntityTypeMapping TypeName="IsTypeOf(SCTModel.SocialContact)">
        <MappingFragment StoreEntitySet="SocialContacts">
          <ScalarProperty Name="Id" ColumnName="Id" />
          <ScalarProperty Name="DateAdded" ColumnName="DateAdded" />
          <ScalarProperty Name="Information" ColumnName="Information" />
          <ComplexProperty Name="DefaultAssociations" TypeName="SCTModel.DefaultAssociations">
            <ScalarProperty Name="DefaultLocationID" ColumnName="DefaultAssociations_DefaultLocationID" />
            <ScalarProperty Name="DefaultEmailID" ColumnName="DefaultAssociations_DefaultEmailID" />
            <ScalarProperty Name="DefaultPhoneNumberID" ColumnName="DefaultAssociations_DefaultPhoneNumberID" />
            <ScalarProperty Name="DefaultWebsiteID" ColumnName="DefaultAssociations_DefaultWebsiteID" />
          </ComplexProperty>
          <ScalarProperty Name="Picture" ColumnName="Picture" />
        </MappingFragment>
      </EntityTypeMapping>
      <EntityTypeMapping TypeName="IsTypeOf(SCTModel.Person)">
        <MappingFragment StoreEntitySet="SocialContacts_Person">
          <ScalarProperty Name="Id" ColumnName="Id" />
          <ScalarProperty Name="DateOfBirth" ColumnName="DateOfBirth" />
          <ScalarProperty Name="FirstName" ColumnName="FirstName" />
          <ScalarProperty Name="LastName" ColumnName="LastName" />
        </MappingFragment>
      </EntityTypeMapping>
      <EntityTypeMapping TypeName="IsTypeOf(SCTModel.Organization)">
        <MappingFragment StoreEntitySet="SocialContacts_Organization">
          <ScalarProperty Name="Id" ColumnName="Id" />
          <ScalarProperty Name="Name" ColumnName="Name" />
          <ScalarProperty Name="DateOfCreation" ColumnName="DateOfCreation" />
        </MappingFragment>
      </EntityTypeMapping>
    </EntitySetMapping>
    <EntitySetMapping Name="Locations">
      <EntityTypeMapping TypeName="IsTypeOf(SCTModel.Location)">
        <MappingFragment StoreEntitySet="Locations">
          <ScalarProperty Name="Id" ColumnName="Id" />
          <ScalarProperty Name="City" ColumnName="City" />
          <ScalarProperty Name="State" ColumnName="State" />
          <ScalarProperty Name="ZIP" ColumnName="ZIP" />
          <ScalarProperty Name="Country" ColumnName="Country" />
          <ComplexProperty Name="Address" TypeName="SCTModel.Address">
            <ScalarProperty Name="Street" ColumnName="Address_Street" />
            <ScalarProperty Name="Apartment" ColumnName="Address_Apartment" />
            <ScalarProperty Name="HouseNumber" ColumnName="Address_HouseNumber" />
          </ComplexProperty>
        </MappingFragment>
      </EntityTypeMapping>
    </EntitySetMapping>
    <EntitySetMapping Name="PhoneNumbers">
      <EntityTypeMapping TypeName="IsTypeOf(SCTModel.PhoneNumber)">
        <MappingFragment StoreEntitySet="PhoneNumbers">
          <ScalarProperty Name="Id" ColumnName="Id" />
          <ScalarProperty Name="Number" ColumnName="Number" />
          <ScalarProperty Name="PhoneType" ColumnName="PhoneType" />
        </MappingFragment>
      </EntityTypeMapping>
    </EntitySetMapping>
    <EntitySetMapping Name="Emails">
      <EntityTypeMapping TypeName="IsTypeOf(SCTModel.Email)">
        <MappingFragment StoreEntitySet="Emails">
          <ScalarProperty Name="Id" ColumnName="Id" />
          <ScalarProperty Name="DomainName" ColumnName="DomainName" />
          <ScalarProperty Name="UserName" ColumnName="UserName" />
        </MappingFragment>
      </EntityTypeMapping>
    </EntitySetMapping>
    <EntitySetMapping Name="Websites">
      <EntityTypeMapping TypeName="IsTypeOf(SCTModel.Website)">
        <MappingFragment StoreEntitySet="Websites">
          <ScalarProperty Name="Id" ColumnName="Id" />
          <ScalarProperty Name="URL" ColumnName="URL" />
        </MappingFragment>
      </EntityTypeMapping>
    </EntitySetMapping>
    <AssociationSetMapping Name="SocialContactWebsite" TypeName="SCTModel.SocialContactWebsite" StoreEntitySet="SocialContactWebsite">
      <EndProperty Name="SocialContact">
        <ScalarProperty Name="Id" ColumnName="SocialContacts_Id" />
      </EndProperty>
      <EndProperty Name="Website">
        <ScalarProperty Name="Id" ColumnName="Websites_Id" />
      </EndProperty>
    </AssociationSetMapping>
    <AssociationSetMapping Name="SocialContactPhoneNumber" TypeName="SCTModel.SocialContactPhoneNumber" StoreEntitySet="SocialContactPhoneNumber">
      <EndProperty Name="SocialContact">
        <ScalarProperty Name="Id" ColumnName="SocialContacts_Id" />
      </EndProperty>
      <EndProperty Name="PhoneNumber">
        <ScalarProperty Name="Id" ColumnName="PhoneNumbers_Id" />
      </EndProperty>
    </AssociationSetMapping>
    <AssociationSetMapping Name="SocialContactEmail" TypeName="SCTModel.SocialContactEmail" StoreEntitySet="SocialContactEmail">
      <EndProperty Name="SocialContact">
        <ScalarProperty Name="Id" ColumnName="SocialContacts_Id" />
      </EndProperty>
      <EndProperty Name="Email">
        <ScalarProperty Name="Id" ColumnName="Emails_Id" />
      </EndProperty>
    </AssociationSetMapping>
    <AssociationSetMapping Name="SocialContactLocation" TypeName="SCTModel.SocialContactLocation" StoreEntitySet="SocialContactLocation">
      <EndProperty Name="SocialContact">
        <ScalarProperty Name="Id" ColumnName="SocialContacts_Id" />
      </EndProperty>
      <EndProperty Name="Location">
        <ScalarProperty Name="Id" ColumnName="Locations_Id" />
      </EndProperty>
    </AssociationSetMapping>
  </EntityContainerMapping>
</Mapping>

需要注意的是，上述代码仅在 MSL 文件的 XML 存储为单独的文件时（例如当元数据由宿主项目复制到输出路径顶部时）或 XML 已经可用时才有效。我仍然需要知道的是，当 MSL 信息仅作为程序集资源存储时，如何提取它。

对于那些想要提供更多意见的人，请记住，任何通用解决方案都应适用于任何版本的 .NET（至少 4.0 及更高版本）——包括 4.7 之前的版本。它还应该能够处理复杂的属性表达式。

Answer 5

我有点困惑，为什么 SQL Server 中使用的原始表名和列名与模型的实体名和属性名不匹配。除了用于提供多对多映射的表外，（通常）您的对象名称/属性与表名和列名之间应该有直接对应关系。

话虽如此，实体框架是一个 ORM。该框架的全部目的是为您的数据库提供面向对象的视图，并抽象出必须直接与关系数据库交互。 EF 并不是真的要让你绕过框架，据我所知，你想要做的事情是不可能的。 （但是，如果我错了，这是我今天学到的新东西，我会相应地删除或编辑这个答案。）