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<h1>Xml Import-Export In .NET</h1>
<p>One of the most widely used platform independent formats of data exchange today is xml.</p>
<p>Db4o
does not provide any specific API to be used for XML import/export, but
with the variety of XML serialization tools available for Java and .NET
(freeware and licensed) this is not really necessary. </p>
<p>All that you need to export your database/query results is:</p>
<ol>
<li value="1">Retrieve objects from the database.</li>
<li value="2">Serialize them in XML format (using language, or external tools, or your own serializing software).</li>
<li value="3">Save XML stream (to a disc location, into memory, into another database).</li>
</ol>
<p>Import process is just the reverse:</p>
<ol>
<li value="1">Read XML stream</li>
<li value="2">Create an objects from XML</li>
<li value="3">Save objects to db4o</li>
</ol>
<p>Let's go through a simple example. We will use .NET XmlSerializer. (You can use
any other XML serialization tool, which is able to serialize/deserialize
classes).</p>
<p>First, let's prepare a database:</p>
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<pre class="prettyprint" xml:space="preserve">SerializeExample.cs: SetObjects
private static void SetObjects()
{
File.Delete(Db4oFileName);
IObjectContainer db = Db4oFactory.OpenFile(Db4oFileName);
try
{
Car car = new Car("BMW", new Pilot("Rubens Barrichello"));
db.Store(car);
car = new Car("Ferrari", new Pilot("Michael Schumacher"));
db.Store(car);
}
finally
{
db.Close();
}
}</pre>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<pre class="prettyprint lang-vb" xml:space="preserve">SerializeExample.vb: SetObjects
Private Shared Sub SetObjects()
File.Delete(Db4oFileName)
Dim db As IObjectContainer = Db4oFactory.OpenFile(Db4oFileName)
Try
Dim car As Car = New Car("BMW", New Pilot("Rubens Barrichello"))
db.Store(car)
car = New Car("Ferrari", New Pilot("Michael Schumacher"))
db.Store(car)
Finally
db.Close()
End Try
End Sub</pre>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>We will save the database to XML file "formula1.xml":</p>
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<pre class="prettyprint" xml:space="preserve">SerializeExample.cs: ExportToXml
private static void ExportToXml()
{
XmlSerializer carSerializer = new XmlSerializer(typeof(Car[]));
StreamWriter xmlWriter = new StreamWriter(XmlFileName);
IObjectContainer db = Db4oFactory.OpenFile(Db4oFileName);
try
{
IObjectSet result = db.QueryByExample(typeof(Car));
Car[] cars = new Car[result.Size()];
for (int i = 0; i < result.Size(); i++)
{
Car car = (Car)result[i];
cars.SetValue(car,i);
}
carSerializer.Serialize(xmlWriter, cars);
xmlWriter.Close();
}
finally
{
db.Close();
}
}</pre>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<pre class="prettyprint lang-vb" xml:space="preserve">SerializeExample.vb: ExportToXml
Private Shared Sub ExportToXml()
Dim carSerializer As XmlSerializer = _
New XmlSerializer(GetType(Car()))
Dim xmlWriter As StreamWriter = New StreamWriter(XmlFileName)
Dim db As IObjectContainer = Db4oFactory. _
OpenFile(Db4oFileName)
Try
Dim result As IObjectSet = db.QueryByExample(GetType(Car))
Dim cars() As Car = New Car(result.Size()) {}
Dim i As Integer
For i = 0 To result.Size() - 1 Step i + 1
Dim car As Car = CType(result(i), Car)
cars.SetValue(car, i)
Next
carSerializer.Serialize(xmlWriter, cars)
xmlWriter.Close()
Finally
db.Close()
End Try
End Sub</pre>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>After the method executes all car objects from the database will be stored in
the export file as an array. Note that child objects (Pilot) are stored as well
without any additional settings. You can check the created XML file to see how
it looks like.</p>
<p>Now we can clean the database and try to recreate it from the
XML file:</p>
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<pre class="prettyprint" xml:space="preserve">SerializeExample.cs: ImportFromXml
private static void ImportFromXml()
{
File.Delete(Db4oFileName);
XmlSerializer carSerializer = new XmlSerializer(typeof(Car[]));
FileStream xmlFileStream = new FileStream(XmlFileName, FileMode.Open);
Car[] cars = (Car[])carSerializer.Deserialize(xmlFileStream);
IObjectContainer db;
foreach (Car car in cars)
{
db = Db4oFactory.OpenFile(Db4oFileName);
try
{
Car newCar = (Car)car;
db.Store(newCar);
}
finally
{
db.Close();
}
}
db = Db4oFactory.OpenFile(Db4oFileName);
try
{
IObjectSet result = db.QueryByExample(typeof(Pilot));
ListResult(result);
result = db.QueryByExample(typeof(Car));
ListResult(result);
}
finally
{
db.Close();
}
}</pre>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<pre class="prettyprint lang-vb" xml:space="preserve">SerializeExample.vb: ImportFromXml
Private Shared Sub ImportFromXml()
File.Delete(Db4oFileName)
Dim carSerializer As XmlSerializer = New _
XmlSerializer(GetType(Car()))
Dim xmlFileStream As FileStream = New _
FileStream(XmlFileName, FileMode.Open)
Dim cars() As Car = CType(carSerializer. _
Deserialize(xmlFileStream), Car())
Dim db As IObjectContainer
Dim car As Car
For Each car In cars
db = Db4oFactory.OpenFile(Db4oFileName)
Try
Dim newCar As Car = CType(car, Car)
db.Store(newCar)
Finally
db.Close()
End Try
Next
db = Db4oFactory.OpenFile(Db4oFileName)
Try
Dim result As IObjectSet = db.QueryByExample(GetType(Pilot))
ListResult(result)
result = db.QueryByExample(GetType(Car))
ListResult(result)
Finally
db.Close()
End Try
End Sub</pre>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>Easy,
isn't it? Obviously there is much more about XML serialization:
renaming fields, storing collections, selective persistence etc. You
should be able to find detailed description together with the
serialization library, which you will use.</p>
<p MadCap:conditions="Primary.Online">Download example code:</p>
<p MadCap:conditions="Primary.Online">
<MadCap:conditionalText MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages"><a href="serializingvb.zip">VB.NET </a>
</MadCap:conditionalText>
<MadCap:conditionalText MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages"><a href="serializingcs.zip">c# </a>
</MadCap:conditionalText>
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