Server-Side Pagination

Currently we do all pagination client-side which won't be possible to keep doing as we accumulate more data

This will be needed for:

• Request Management System
• Organisation Registry
• Volunteer Registry

fractalis has offered to look at this

Status

• The Back-end is now done for HTML representation
• The Back-end was already done for JSON representation, now done in the dataTables way
• The Front-end is done: 50 records at a time :)
• ToDo:
  • Push from Dev to Live
  • Render as .represent
  • Return to Live (1 line in Controller functions: response.s3.pagination = True)
  • Sort Columns (orderby)
  • Search (filtering)
  • XSLT to generate dataTables-compliant JSON?

Front-end implementation

• ​http://datatables.net/examples/data_sources/server_side.html
• ​http://datatables.net/usage/server-side
• We'll also need to hand-off the Searching & Sorting!

Client-side, we need to add these options to views/dataTables.html [make them Optional per-REST Controller?]:

    "bProcessing": true,
    "bServerSide": true,
    "sAjaxSource": "{{=URL(r=request, c='module', r='resource', vars={'...':'...'})}}"

Server-side, we need to understand these vars:

# Pagination
iDisplayStart - maps to 'start'
iDisplayLength - maps to 'limit'
# Ordering
iSortCol_0
iSortingCols
iSortCol_x
iSortDir_x
# Filtering (Search) - across all fields!
sSearch

response should be sent in this format:

{
"sEcho": 1,
"aaData": [
    [row1.id, row1.field2, ...],
    [row2.id, row2.field2, ...],
    [row3.id, row3.field2, ...]
],
"iTotalRecords": 3,
"iTotalDisplayRecords": 3
}

e.g. using a function like:

def callback():
    iDisplayStart = int(request.vars.iDisplayStart)
    iDisplayLength = int(request.vars.iDisplayLength)
    from gluon.serializers import json
    _table = '%s_%s' % (request.controller, request.function)
    table = db[_table]
    query = (table.id > 0)
    rows = db(query).select(limitby = (iDisplayStart, iDisplayStart + iDisplayLength))
    r = dict(sEcho = 1,
           iTotalRecords = len(rows),
           iTotalDisplayRecords = len(rows),
           aaData = [[row[f] for f in table.fields if table[f].readable] for row in rows])
    return json(r)

Problems:

• ​http://datatables.net/forums/comments.php?DiscussionID=1156&page=1#Item_1

JSON Back-end implementation

• Support already present in modules\s3xrc.py
  • http://S3_PUBLIC_URL/module/resource.json?limit=x&start=y
• needs patching for dataTables-expectations:

  if "start" in self.request.vars:
      start = int(self.request.vars["start"])
  elif "iDisplayStart" in self.request.vars:
      # dataTables
      start = int(self.request.vars["iDisplayStart"])
  else:
      start = None
  
  if "limit" in self.request.vars:
      limit = int(self.request.vars["limit"])
  elif "iDisplayLength" in self.request.vars:
      # dataTables
      limit = int(self.request.vars["iDisplayLength"])
  else:
      limit = None
  

• actually needs a complete new representation unless this could be done via XSLT!?
  • still needs extension adding to shn_xml_export_formats in models\01_RESTlike_controller.py

HTML Back-end implementation

Patched the models\01_RESTlike_Controller to support http://S3_PUBLIC_URL/module/resource?limit=x&start=y

shn_list()
...
     if request.vars.limit:
        limit = int(request.vars.limit)
        if request.vars.start:
            start = int(request.vars.start)
            limitby = (start, start + limit)
        else:
            limitby = (0, limit)
    else:
        limitby = None
...
items = crud.select(table, query=query,
            ...
            limitby=limitby, 
            ...
            )

Other Options

• Maybe look at the currently-unused modules/webgrid.py.
• pagenav in models\01_RESTlike_Controller seems unused currently...was an older implementation of a webgrid...can probably be removed.
• ExtJS

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Haiti Haiti