Composition
===========

Composition is useful when you have two or more reports sharing common things.

But her is a big diferent from Inheritance: while **inheritance** is start a
report from the point where another one ends, **composition** is about you make
separated things and after compose a report with them.

Example: two reports of Users, one with some fields and other with more fields
and landscape page orientation::

    import os
    cur_dir = os.path.dirname(os.path.abspath(__file__))
    
    from django.contrib.auth.models import User
    
    from reportlab.lib.pagesizes import A4
    from reportlab.lib.units import cm
    from reportlab.lib.enums import TA_CENTER, TA_RIGHT
    
    from geraldo import Report, ReportBand, Label, ObjectValue, SystemField,\
        BAND_WIDTH, landscape
    
    class PageHeaderBand(ReportBand):
        height = 1.3*cm
        elements = [
            SystemField(expression='%(report_title)s', top=0.1*cm, left=0, width=BAND_WIDTH,
                style={'fontName': 'Helvetica-Bold', 'fontSize': 14, 'alignment': TA_CENTER}),
            Label(text="ID", top=0.8*cm, left=0),
            Label(text="Username", top=0.8*cm, left=3*cm),
            Label(text="First name", top=0.8*cm, left=8*cm),
            Label(text="Last name", top=0.8*cm, left=13*cm),
            Label(text="Staff", top=0.8*cm, left=18*cm),
        ]
        borders = {'bottom': True}
    
    class PageFooterBand(ReportBand):
        height = 0.5*cm
        elements = [
            Label(text='Created with Geraldo Reports', top=0.1*cm),
            SystemField(expression='Printed in %(now:%Y, %b %d)s at %(now:%H:%M)s', top=0.1*cm,
                width=BAND_WIDTH, style={'alignment': TA_RIGHT}),
        ]
        borders = {'top': True}
    
    class DetailBand(ReportBand):
        height = 0.7*cm
        elements = [
            ObjectValue(attribute_name='id', top=0, left=0),
            ObjectValue(attribute_name='username', top=0, left=3*cm, display_format='<font size=14 name=Helvetica>%s</font>'),
            ObjectValue(attribute_name='first_name', top=0, left=8*cm),
            ObjectValue(attribute_name='last_name', top=0, left=13*cm),
            ObjectValue(attribute_name='is_staff', top=0, left=18*cm,
                get_value=lambda instance: instance.is_staff and 'Yes' or 'No'),
        ]
    
    class UsersReport(Report):
        """Report 1 class"""
    
        title = 'Users'
    
        band_page_header = PageHeaderBand
        band_page_footer = PageFooterBand
        band_detail = DetailBand
    
    class LandscapeUsersReport(Report):
        """Report 2 class"""
    
        title = 'Users'
        page_size = landscape(A4)
    
        band_page_header = PageHeaderBand
        band_page_footer = PageFooterBand
    
        class band_detail(DetailBand):
            elements = DetailBand.elements+[
                ObjectValue(attribute_name='date_joined', top=0, left=21*cm),
            ]
    
        def __init__(self, *args, **kwargs):
            super(LandscapeUsersReport, self).__init__(*args, **kwargs)
    
            self.band_page_header.elements += [
                Label(text="Date joined", top=0.8*cm, left=21*cm),
                ]
            
            self.band_page_footer.elements[0].text += ' - Landscape'

Generating PDF...

    >>> queryset = User.objects.order_by('id')
    >>> report = UsersReport(queryset=queryset)
    >>> from geraldo.generators import PDFGenerator
    >>> report.generate_by(PDFGenerator, filename=os.path.join(cur_dir, 'output/composition-report.pdf'))

Now generating the composed landscape report

    >>> report = LandscapeUsersReport(queryset=queryset)
    >>> report.generate_by(PDFGenerator, filename=os.path.join(cur_dir, 'output/composition-landscape-report.pdf'))

The Result

- http://geraldo.svn.sourceforge.net/viewvc/geraldo/examples/composition-report.pdf
- http://geraldo.svn.sourceforge.net/viewvc/geraldo/examples/composition-landscape-report.pdf

