title: Why is The navigation property '' declared on type '' has been configured with conflicting multiplicities. error show up?
body: <p>I have an <code>Asp_Users</code> table and a <code>Resource</code> tables. In the Entity Framework world, I have a <code>Asp_Users</code> POCO and a <code>Resource</code> POCO. Moreover, the <code>Resource</code> POCO is abstract and is part of a Table-per-Hierarchy model. The Table-per-Hierarchy model has the abstract <code>Resource</code> POCO and several <code>Concrete</code> POCOs like <code>ILCResource</code> POCO and <code>SectionResource</code> POCO. There is a one-to-many (1 to 0…*) relationship from <code>Asp_Users</code> POCO (one-side) to <code>Resource</code> POCO (many-side). </p>
  
  <p>Here's the relevant part of my aspnet_Users POCO:</p>
  
  <pre><code>public partial class aspnet_Users
  {
      public aspnet_Users() { }
  
      public virtual System.Guid ApplicationId { get; set; }
      public virtual System.Guid UserId { get; set; }
      public virtual string UserName { get; set; }
      public virtual string LoweredUserName { get; set; }
      public virtual string MobileAlias { get; set; }
      public virtual bool IsAnonymous { get; set; }
      public virtual System.DateTime LastActivityDate { get; set; }
  
      public virtual ICollection&lt;Resource&gt; associatedResources { get; set; }
  }
  </code></pre>
  
  <p>Here is my mapping configuration for Asp_Users</p>
  
  <pre><code>public class Aspnet_UsersMap : EntityTypeConfiguration&lt;PerlsData.Domain.aspnet_Users&gt;
  {
      public Aspnet_UsersMap()
      {
          this.ToTable("aspnet_Users", schemaName: "dbo");
  
          this.HasKey(u =&gt; u.UserId);
  
          this.Property(u =&gt; u.UserId)
              .HasColumnName("UserId")
              .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
          this.HasOptional(u =&gt; u.associatedResources);
      }
  } 
  </code></pre>
  
  <p>Here's the relevant part of my abstract Resource POCO class:</p>
  
  <pre><code>public abstract class Resource
  {   
      public Resource(){
         // associatedPerspectives = new HashSet&lt;Perspective&gt;();
      }
  
      public virtual System.Guid ResourceDatabaseID { get; set; }
      public virtual string ResourceName { get; set; }
      public virtual string DescriptionOfResource { get; set; }
      public virtual System.Guid UserId { get; set; }
      public virtual Nullable&lt;System.Guid&gt; DepartmentDatabaseID { get; set; }
      public virtual string ResourceStatus { get; set; }
      public virtual Nullable&lt;short&gt; isRemoved { get; set; }
  
      public virtual Department Department { get; set; }
  
      public virtual System.Guid UserId { get; set; }
      public virtual aspnet_Users aspnet_Users { get; set; }
  
  
      public virtual ICollection&lt;ResourceOverToILCResourcesBridge&gt; associatedResourceOverToILCResourcesBridgeEntry { get; set; }
  }
  </code></pre>
  
  <p>Here is my mapping configuration for Resource:</p>
  
  <pre><code>public class ResourceMap : EntityTypeConfiguration&lt;Resource&gt;
  {
  
      public ResourceMap()
      {
          this.ToTable("Resources", schemaName: "dbo");
  
          this.Property(r =&gt; r.ResourceDatabaseID)
              .HasColumnName("ResourceDatabaseID");
  
          this.HasKey(r =&gt; r.ResourceDatabaseID);
  
          this.Property(x =&gt; x.ResourceDatabaseID)
              .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
          // .StoreGeneratedPattern = StoreGeneratedPattern.Identity;
          this.Property(r =&gt; r.ResourceName)
              .HasColumnName("ResourceName");
  
          this.Map&lt;PerlsData.Domain.OtherItem&gt;(m =&gt; m.Requires("discriminator").HasValue("otheritems"))
          .Map&lt;PerlsData.Domain.Audioitem&gt;(m =&gt; m.Requires("discriminator").HasValue("audioitems"))
          .Map&lt;PerlsData.Domain.Imageitem&gt;(m =&gt; m.Requires("discriminator").HasValue("imageitems"))
          .Map&lt;PerlsData.Domain.Videoitem&gt;(m =&gt; m.Requires("discriminator").HasValue("videoitems"))
          .Map&lt;PerlsData.Domain.UriItem&gt;(m =&gt; m.Requires("discriminator").HasValue("uriitems"))
          .Map&lt;PerlsData.Domain.Documentitem&gt;(m =&gt; m.Requires("discriminator").HasValue("documentitems"))
          .Map&lt;PerlsData.Domain.DatabaseFileItem&gt;(m =&gt; m.Requires("discriminator").HasValue("databasefileitems"));
  
          this.HasOptional(res =&gt; res.associatedResourceOverToILCResourcesBridgeEntry);
  
          this.HasRequired(res =&gt; res.aspnet_Users)
              .WithMany(u =&gt; u.associatedResources)
              .HasForeignKey(res =&gt; res.UserId);
      }
  }
  </code></pre>
  
  <p>Could you please tell me why I am getting the following error?</p>
  
  <blockquote>
    <p>The navigation property 'associatedResources' declared on type
    'PerlsData.Domain.aspnet_Users' has been configured with conflicting
    multiplicities.</p>
  </blockquote>
  
  <p>Please Explain Why it's still NULL after I created the mapping in the POCO class.</p>
  
  <p><img src="https://i.stack.imgur.com/fPXG0.png" alt="enter image description here"></p>