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<h1>Field Refactoring Limitation</h1>
<p>For most cases changing the field type isn't an issue. db4o keeps the old values around and you can access the old values without issues. <a href="field_type_change.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Field Type Change"</a></p>
<p>However there's one limitation to this mechanism. You cannot change the type of a field to its array-type and vice versa. This only applies if it's the same array-type. For example:</p>
<ul>
<li value="1">You cannot change a string field to a string array field and vice versa.</li>
<li value="2">You can change a string field to an int-, object-, etc array. Every type is possible except a string-array.</li>
<li value="3">You can change a string-array to an int-, object etc. Every type is possible except a string.</li>
</ul>
<h2>Refactoring To An Array-Field Step by Step</h2>
<p>When you change the type of a field to its array-type equivalent, you can do this only by copying the old data to a new class. In this example we have a Person-class which has its name in a string field. Now we want to change that to a string array to support multiple names.</p>
<ol>
<li value="1">Create a copy of the Person-class with a new name.</li>
<li value="2">Do the refactoring on the new Person class</li>
<li value="3">Query for old instances of the old Person-class and copy the values over to the new class.</li>
</ol>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IList<PersonOld> oldPersons = container.Query<PersonOld>();
foreach (PersonOld old in oldPersons)
{
PersonNew newPerson = new PersonNew();
newPerson.Name = new string[] {old.Name};
container.Store(newPerson);
container.Delete(old);
}</pre>
<div class="codesnippet-meta">ChangeArrayType.cs: Copy the string-field to the new string-array field
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Dim oldPersons As IList(Of PersonOld) = container.Query(Of PersonOld)()
For Each old As PersonOld In oldPersons
Dim newPerson As New PersonNew()
newPerson.Name = New String() {old.Name}
container.Store(newPerson)
container.Delete(old)
Next</pre>
<div class="codesnippet-meta">ChangeArrayType.vb: Copy the string-field to the new string-array field
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<p>Note that this example doesn't change existing references from the old instances to the new ones. You need to do this manually as well.</p>
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