# Custom Legacy Type Handler

{% hint style="warning" %}
**This is the manual for older MicroStream versions (Version < 5.0).**

**The new documentation (Version >= 5.0) is located at:**

[https://docs.microstream.one/](https://docs.microstream.one/manual)
{% endhint %}

In addition to the methods for legacy type mapping described in chapter [Legacy Type Mapping](/2.2/data-store/legacy-type-mapping.md) there is also the possibility to implement custom legacy type handlers. Those handlers are the most flexible way to do the mapping from old to new types.

The basic interface that has to be implemented is `one.microstream.persistence.types.PersistenceLegacyTypeHandler.`

Fortunately the standard persistence implementation provides the abstract class `one.microstream.persistence.binary.types.BinaryLegacyTypeHandler.AbstractCustom` that should be sufficient to start with a custom implementation in most cases.

{% hint style="info" %}
See the example **customLegacyTypeHandler** on [GitHub](https://github.com/microstream-one/examples/tree/2.2/customLegacyTypeHandler)
{% endhint %}

{% hint style="info" %}
Please note the this example requires manual code modifications as described in it's main class.
{% endhint %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://manual.docs.microstream.one/2.2/data-store/customizing/custom-legacy-type-handler.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.