title: devart oracle 9.3- entity framework 7 ( or core 1) Mapping can't recognize decimal at visual studio 2017
body: <p>I am working on a .Net Core class library project.I use Devart entity framework core to connect oracle database. I use devart's oracle mapping methods at link
   <a href="http://blog.devart.com/entity-framework-core-1-entity-framework-7-support.html" rel="nofollow noreferrer">http://blog.devart.com/entity-framework-core-1-entity-framework-7-support.html</a></p>
  
  <p>I can get datas successfully when type of columns of table is string. But, if type of columns of table is decimal, complier gives me error below:</p>
  
  <pre><code>Severity    Code    Description Project File    Line    Suppression State
  Error   CS0452  The type 'decimal?' must be a reference type in order to use it as parameter 'TEntity' in the generic type or method 'OraclePropertyBuilderExtensions.ForOracleHasColumnName&lt;TEntity&gt;(PropertyBuilder&lt;TEntity&gt;, string)'.
  </code></pre>
  
  <p>my mapping function is:</p>
  
  <pre><code> private void MyTableMapping(ModelBuilder modelBuilder)
          {
              modelBuilder.Entity&lt;MyTable&gt;().ForOracleToTable(@"MyTable");
              modelBuilder.Entity&lt;MyTable&gt;().Property&lt;string&gt;(x =&gt; x.SIRKETID).ForOracleHasColumnName(@"SIRKET_ID").ForOracleHasColumnType(@"VARCHAR2").ValueGeneratedNever().HasMaxLength(2);//this  line is ok
              modelBuilder.Entity&lt;MyTable&gt;().Property&lt;decimal&gt;(x =&gt; x.ID).ForOracleHasColumnName(@"ID").ForOracleHasColumnType(@"NUMBER").IsRequired().ValueGeneratedOnAdd();//this  line gives error
           }
  </code></pre>
  
  <p>Sorry for my low English.</p>