Wrap a legacy or third party database?
Base4 is ideal for taking a legacy
or third party database and re-exposing it with a simple and consistent API. To
do this you need to create a legacy schema, which simply involves registering all
the types from your old database with Base4.
To illustrate how this
works imagine you have a very simple database called [bugs] database. In that database you have a number of tables
but only 2 that are of interest at the moment, namely the [bugs].[dbo].[bug] table and the [bugs].[dbo].[person]
table. On the same SQL server you also have a Base4 database called
[base4_default].
So logically things look like this:
You need to start by
registering a Schema with Base4 that includes 2 Types one for the [bugs].[dbo].[bug] table and one for the [bugs].[dbo].[person] table.
This is done like this:
<Schema
Name="Bugs.dll" uri="http://www.base4.net/Schemas/Bugs.xml"
version="1">
<!-- A list
of all the other schemas that this depends on or references -->
<References>
<!-- References the builtin Base4.Storage.dll
schema-->
<Reference
Name="Base4.Storage.dll" dirty="True"
inDatabase="False"
uri="http://www.base4.net/schemas/Base4.Storage.xml"
version="1" />
</References>
<Types>
<!-- Register
the [bugs].[dbo].[Person] table with Base4 -->
<Type
FullName="Bugs.Person" source="[bugs].[dbo].[Person]"
baseName="Base4.Storage.ItemImpl"
keyProperty="ID"
version="1" readOnly="True" >
<Property
name="ID" typeName="System.Int32"
nullable="False"
unique="True" source="iID"/>
<Property
name="Firstname" typeName="System.String" length="100"
source="sFirstname"/>
<Property
name="Surname" typeName="System.String" length="100"
source="sSurname"/>
</Type>
<!-- Register
the [bugs].[dbo].[Bug] table with Base4 -->
<Type
FullName="Bugs.Bug" source="[bugs].[dbo].[Bug]"
baseName="Base4.Storage.ItemImpl"
keyProperty="ID"
version="1" readOnly="True" >
<Property
name="ID" typeName="System.Int32"
nullable="False"
unique="True" source="ixBug"/>
<Property
name="Open" typeName="System.Int32"
source="fOpen" nullable="True"/>
<Property
name="Opened" typeName="System.DateTime"
source="dtOpened" nullable="True"/>
<Property
name="Title" typeName="System.String"
source="sTitle" nullable="True"
length="128"/>
<Property
name="Project" typeName=" System.Int32"
source="ixProject" nullable="True"/>
<Property
name="Area" typeName=" System.Int32"
source="ixArea" nullable="True"/>
<Property
name="OpenedBy" typeName="Bugs.Person"
source="ixPersonOpenedBy" nullable="True"/>
<Property
name="AssignedTo" typeName="Bugs.Person"
source="ixPersonAssignedTo" nullable="True"/>
<Property
name="Status" typeName="System.Int32"
source="ixStatus" nullable="True"/>
<Property
name="Priority" typeName="System.Int32"
source="ixPriority" nullable="True"/>
</Type>
</Types>
</Schema>
Notice the use of the
source attribute in the Type element to map a new Type to an existing table. The
source is in an MSSQL full table path in the
form
[database].[owner].[table] and is used by Base4
to link from the Base4 database to another database on the same server.
Also in the above example
we have taken this opportunity to ensure the resulting Base4 types are more readable
and friendly by using the source
attribute of the property to point to the existing field but to use the new
name specified instead.
Once we have done this
Base4 will create views
in the Base4 database that encapsulate all access to the two tables from the
[bugs] database, like this:
At this point is completely possible
to query the Base4 for information in the legacy database like this:
using System;
using System.Collections.Generic;
using System.Windows.Forms;
using Base4.Storage;
using Bugs;
namespace Base4.Storage.Quickstart
{
static class
Program
{
/// <summary>
/// Find all Bugs
assigned to Alex
/// </summary>
static void
QueryTheBugsDatabase()
{
foreach (Bug
bug in StorageContext.Find<Bug>(Bug.Fields.AssignedTo.Firstname
== "Alex"))
{
Console.WriteLine(bug.Title);
}
}
}
}