Question

I am using entity framework 4.1, an edmx mapping file is used to generate poco classes using T4 templates.

How can I get a name of the data base column out of object context for my poco entity properties (if it is possible at all).

I believe the mapping between properties and columns should be in one of the containers:

var container = objectContext.MetadataWorkspace
    .GetEntityContainer(objectContext.DefaultContainerName, DataSpace.CSpace);
...

But I was not able to identify a link between CSpase and SSpace, it looks like CSSpase might do the job, but this container is empty.

Any ideas?

Answer 1

I used a mixed approached to get the mapping information (we have to implement custom data reader/writer for certain types):

1. First get EntityType object to extract meta information for your POCO type:

   public static EntityType GetEntityTypeForPoco(this ObjectContext context, 
                                                            Type pocoEntityType)
   {
       EntityType entityType 
                = context.MetadataWorkspace.GetItem<EntityType>
                  (pocoEntityType.FullName, DataSpace.OSpace);
   
       return (EntityType)context.MetadataWorkspace
              .GetEdmSpaceType((StructuralType)entityType);
   }
   

2. Read mapping XML document: this part is basically hardcoded, mapping xml document is saved in the assembly where edmx file is, it’s called [your_edmx_file_name].msl

   currentMslSchemaDocument = new StreamReader(
               Assembly.GetExecutingAssembly().
               GetManifestResourceStream(CurrentMslSchemaDocumentName)
             ).ReadToEnd();
   

3. Read property to column mapping from XML document:

   var mappingFragments = MslSchemaDocument
   .Descendants(XName.Get(ElementNameEntityTypeMapping, NamespaceNameMsl))
   .Where(mp => (mp.Attributes(AttributeNameTypeName).Any() 
   && mp.Attribute(AttributeNameTypeName).Value == entityTypeModelName));
   
   if (mappingFragments.Count() == 0)
   {
       throw new Exception(String.Format("Entity mapping {0} is not found in the given schema stream", entityTypeModelName));
   }
   
   //theoretically could be several fragments mapping one entity ytpe to several table
   XElement mappingFragment = mappingFragments.First();
   
   string tableName = mappingFragment.Descendants(XName.Get(ElementNameMappingFragment, NamespaceNameMsl))
   .First().Attribute(AttributeNameStoreEntitySet).Value;
   
   List<KeyValuePair<string, string>> propertyColumnMappingList = new List<KeyValuePair<string, string>>();
   
   foreach (var xScalarProperty in mappingFragment.Descendants(XName.Get(ElementNameScalarProperty, NamespaceNameMsl)))
   {
      propertyColumnMappingList.Add(new KeyValuePair<string, string>(xScalarProperty.Attribute(AttributeNameName).Value,
               xScalarProperty.Attribute(AttributeNameColumnName).Value));
   }