title: Entity Framework Core: Owned type that has navigation properties
body: <p>I have some classes:</p>
  <pre><code>public class Project 
  {
       public TimeLine TimeLine { get; set; };
  }
  
  public class TimeLine 
  {
       public ICollection&lt;TimeLinePhases&gt; TimeLinePhases { get; set; };
  }
  
  public TimeLinePhase 
  {
  }
  </code></pre>
  <p>The class <code>Project</code> owns <code>TimeLine</code> and this all works fine until I specify the navigation between <code>TimeLine</code> and <code>TimeLinePhase</code>.</p>
  <p>Fluent API code that specifies <code>TimeLine</code> is owned:</p>
  <pre><code>  builder.Owned&lt;TimeLine&gt;();
    builder.entity&lt;Project&gt;().OwnsOne(p =&gt; p.TimeLine);
  </code></pre>
  <p>I get this error:</p>
  <blockquote>
  <p>InvalidOperationException: Unable to determine the relationship represented by navigation 'TimeLine.TimeLinePhase' of type 'ICollection'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.</p>
  </blockquote>
  <p>So then I specify the relation between <code>TimeLine</code> and <code>TimeLinePhase</code> like this:</p>
  <pre><code>builder
          .Entity&lt;TimeLine&gt;()
          .HasMany(t =&gt; t.TimeLinePhase)
          .WithOne()
          .IsRequired(false);
  </code></pre>
  <p>But now I get this error:</p>
  <blockquote>
  <p>The entity type 'TimeLine' cannot be configured as non-owned because it has already been configured as a owned. Use the nested builder in <code>OwnsOne</code> or <code>OwnsMany</code> on the owner entity type builder to further configure this type</p>
  </blockquote>
  <p>How can I have <code>TimeLine</code> as an owned type, and still have the relation between <code>TimeLine</code> and <code>TimeLinePhases</code>?</p>