无法加载指定的元数据资料Unable to load the specified metadata resource

在应用ADO.NET Entity Framework构建Application时呈现如下异常。Solution 中有2个项目，一个为Windows Form项目，另一个为Class Library 项目，包含ADO.NET Entity Data Model。Windows Form 项目增长对Class Library 项目标引用。

异常信息：

System.Data.MetadataException was unhandled

Message="Unable to load the specified metadata resource."

Source="System.Data.Entity"

StackTrace:

       at System.Data.Metadata.Edm.MetadataArtifactLoaderCompositeResource.LoadResources （String assemblyName， String resourceName， ICollection`1 uriRegistry， MetadataArtifactAssemblyResolver resolver）

       at System.Data.Metadata.Edm.MetadataArtifactLoaderCompositeResource.CreateResourceLoader（String path， ExtensionCheck extensionCheck， String validExtension， ICollection`1 uriRegistry， MetadataArtifactAssemblyResolver resolver）

       at System.Data.Metadata.Edm.MetadataArtifactLoader.Create（String path， ExtensionCheck extensionCheck， String validExtension， ICollection`1 uriRegistry， MetadataArtifactAssemblyResolver resolver）

       at System.Data.EntityClient.EntityConnection.SplitPaths（String paths）

       at System.Data.EntityClient.EntityConnection.GetMetadataWorkspace（Boolean initializeAllCollections）

       at System.Data.EntityClient.EntityConnection.InitializeMetadata（DbConnection newConnection， DbConnection originalConnection， Boolean closeOriginalConnectionOnFailure）

       at System.Data.EntityClient.EntityConnection.Open（）

在Windows Form 项目中呈现异常的代码：

            string customerID = txtCustomerID.Text.Trim（）;

            // Contains a reference to an Entity Data Model （EDM） and a data source connection.

            using （EntityConnection cn = new EntityConnection（"Name=NorthwindEntities"））

            {

                cn.Open（）;

                EntityCommand cmd = cn.CreateCommand（）;

                cmd.CommandText =

                     "SELECT VALUE c FROM NorthwindEntities.Customers "+

                     "AS c WHERE c.CustomerID = ＠customerID";

                cmd.Parameters.AddWithValue（"customerID"， customerID）;

                DbDataReader rdr = cmd.uteReader（CommandBehavior.SequentialAccess）;

                while （rdr.Read（））

                    Console.WriteLine（rdr["CompanyName"].ToString（））;

                rdr.Close（）;

            }

上述代码行 cn.Open（）; 抛出异常Exception - Unable to load the specified metadata resource。经搜检，题目呈如今App.config 设备文件（该设备文件在应用ADO.NET Entity Data Model领导时主动添加），

ADO.NET Entity Data Model领导主动添加的Connection String：

< configuration >

< connectionStrings >

    < add name = "NorthwindEntities" connectionString="metadata=res://*/NorthwindDB.csdl|res://*/NorthwindDB.ssdl|res://*/NorthwindDB.msl; provider=System.Data.SqlClient;provider connection string=&quot;Data Source=localhost;Initial Catalog=Northwind;Integrated Security=True;MultipleActiveResultSets=True&quot;"providerName="System.Data.EntityClient" />

</ connectionStrings >

</ configuration >

须要将上方connectionStrings 设备节中的* 批改为Class Library 项目标Assembly Name。批改后的示例App.config 如下：

< configuration >

< connectionStrings >

    < add name = "NorthwindEntities" connectionString=" metadata= res://NorthwindEDM/NorthwindModel.csdl|res://NorthwindEDM/NorthwindModel.ssdl|res://NorthwindEDM/NorthwindModel.msl; provider=System.Data.SqlClient;provider connection string=&quot;Data Source=localhost;Initial Catalog=Northwind;Integrated Security=True;MultipleActiveResultSets=True&quot;"providerName="System.Data.EntityClient" />

</ connectionStrings >

</ configuration

    The problem sometimes occurs with the Entity Framework where it gives an array of errors when doing simple operations. For example， I received an error about not being able to &＃8220;unable to load the specified metadata resource&＃8221;. Uh， the connection string information is right in the config file! The problem often can be resolved simply by:

1. open the EDMX file in the designer mode
2. go to the properties of the EDMX
3. set the Metadata Artifact Processing property to &＃8220;Copy to Output&＃8221;
4. build the project
5. 然后从输出目次将*.msl.*.ssdl，*.csdl文件拷贝到应用法度目次底下即可。呵呵（估计很多人这里失足！）