[[TOC]]

= Generating MOLGENIS from scratch =
We will generate a new MOLGENIS by the example of a simple Address Book application:

a simple database having “Contacts” entities that each can have zero or more “Addresses”:

[[Image(address-book-screenshot.JPG)]]

== 1. Create the data model XML[[BR]] ==
Create a new xml file ‘addressbook_db.xml’ in the root of you application. This file will contain the MOLGENIS model. Use the following template:

{{{
#!xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE molgenis PUBLIC "MOLGENIS 1.0" "http://molgenis.sourceforge.net/dtd/molgenis_v_1_0.dtd">
<molgenis name="addressbook">

</molgenis>
}}}

== 2. Add a “Contact” data type. ==
{{{
#!xml
<molgenis name="addressbook">
  <entity name="Contact">
		
  </entity>
</molgenis>
}}}

== 3. Add properties to the “Contact” data type. ==
 * A unique, automatic numeric identifier field that MOLGENIS will use to refer contacts. 
{{{
#!xml
<field name="contact_id" type="autoid"/>
}}}
 * A required and unique string field ‘displayname’ to have a unique label to find Contacts by. Note that if you provide no ‘type’ then type=”string” is implied.
{{{
#!xml
<field name="displayname" unique="true"/>
}}}
 * Optional (‘nillable’) string fields for firstname, lastname and midinitials:
{{{
#!xml
<field name="firstname" nillable="true"/>
<field name="midinitials" nillable="true"/>
<field name="lastname" nillable="true"/>
}}}
 * An optional field of type date for birthday:
{{{
#!xml
<field name="birthday" type="date" nillable="true"/>
}}}

== 4. Similarly create a “Address” data type (to keep it simple we only do phone numbers): ==
 * Entity address
{{{
!xml
<entity name="Address">
}}}
 * A unique, automatic numeric identifier field that MOLGENIS will use to refer addresses. 
{{{
!xml
<field name="address_id" type="autoid"/>
}}}
 * Add the phone number field:
{{{
#!xml
<field name="phone"/>
}}}
 * Add a field where the user can choose from an enumeration of options whether the address is ‘home’,’work’,or ‘mobile’:
{{{
#!xml
<field name="address_type" type="enum" enum_options="[home,work,mobile]"/>
}}}

== 5.	Finally we need to link the Addresses to each Contact. ==
 * In the Address entity create a [http://en.wikipedia.org/wiki/Foreign_key ForeignKey] reference to Contact
{{{
#!xml
<field name="contact" type="xref"     
         xref_field="Contact.contact_id"       
         xref_label="displayname"/>
</entity>
}}}
Note that the xref_field refers to unique field ‘contact_id’ in entity ‘Contact’. The xref_label attribute indicates that we want to view references to Contact by ‘displayname’ name instead of the numeric id.  

Use of a meaningless numeric ‘id’ next to a meaningful ‘label’ enables us to change the ‘displayname’ name on Contact without the problem of also having to change this on each Address that refers to this contact.