> For the complete documentation index, see [llms.txt](https://docs.umbraco.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.umbraco.com/umbraco-ui-builder/collections/entity-identifier-converters.md).

# Entity Identifier Converters

Using Umbraco entities as reference with an UI Builder collection

Umbraco stores identifiers in UDI format for most Umbraco object types.

You can read more about them in the [UDI Identifiers](https://docs.umbraco.com/umbraco-cms/develop-with-umbraco/templating-and-rendering/querying/udi-identifiers) section of the documentation.

If you want to reference an Umbraco object in your model and retrieve its `Integer` or `Guid` value, you must convert the `UDI` value.

Use one of UI Builder's converters - `EntityIdentifierToIntTypeConverter` or `EntityIdentifierToGuidTypeConverter`. Add it as a `[TypeConverterAttribute]` to your model's foreign key property.

An entity that references an Umbraco object would look like this:

```csharp
    [TableName(TableName)]
    [PrimaryKey("Id")]
    public class MemberReview
    {
        public const string TableName = "MemberReview";

        [PrimaryKeyColumn]
        public int Id { get; set; }

        public string Title { get; set; }

        public string Content { get; set; }

        [TypeConverter(typeof(EntityIdentifierToIntTypeConverter))]
        public int MemberId { get; set; }
    }
```

You can also create a custom type converter. UI Builder will handle data persistence automatically.


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