Assign special dbf to shapefile

[Stephen Woodbridge]

The only way that I know of to do runtime joins in mapserver is to use
PostGIS. You might be able to do something with gdal, but I think it is
very slow.  I have requested support for runtime shapefile joins to
either DBF or MySQL multiple times and nothing has happened in that
direction. Basically, it would be very slow because for each object in
the shapefile, you would have to scan the whole DBF file, because there
are no indexes support for DBF files, or the developers would have to
build DBF indexing support into mapserver. For Mysql, you could index
the columns, but you would still need to make a separate query for every
object in the shapefile.

In PostGIS, since you have all the data in the database to start with
you can make one query for the layer and do the join in that query, then
you only have to fetch back the objects to render.

-Steve W.

Holger Floerke wrote:
> Hi Jacob,
>
>
>>Why would you not want to join them?
>
> If the information I would like to present is evaluated at runtime, I have
> to produce a full set of ".shp", ".dbf", "sbx", "sbn", and ".shx" files. The
> shapes always stays the same, but the data is extracted from a database on a
> user's query. I would like to save space by not copying the shape
> information every time.
>
>
>>unless if you created a join on a dbf, and accessed it separately.
>
> Is it possible to join external data sources (one or more dbf-files or
> oci-sources) to shape files at runtime with the mapserver-api?
>
> HolgeR
>
>
> Jacob Delfos schrieb:
>
>
>>Holger,
>>
>>Correct me if I'm wrong, but that would be redefining the definition of
>>a shapefile. As far as I know, a "shapefile" is not the .shp file, but
>>the collection of ".shp", ".dbf", "sbx", "sbn", and ".shx" files. I
>>think you'd have to seriously hack the source of mapserver to do that,
>>unless if you created a join on a dbf, and accessed it separately.
>>
>>Why would you not want to join them? If you have access to MS Excel, it
>>would be as simple as copying a column across. No doubt other software
>>can do the same thing. You would have access to both attributes in one
>>shapefile. What is the actual problem that causes you not to want to
>>have two shapefiles, and not to want to join the attributes?
>>
>>regards,
>>
>>Jacob
>>
>>
>>-----Original Message-----
>>From: UMN MapServer Users List
>>To: MAPSERVER-USERS at LISTS.UMN.EDU
>>Sent: 1/7/2005 9:03 PM
>>Subject: [UMN_MAPSERVER-USERS] Assign special dbf to shapefile
>>
>>Hi all,
>>
>>am I able to assign a special dbf-file to a shape file? For example
>>rendering the 'airports.shp', but using data from
>>'airports_passengers.dbf'
>>and not from 'airports.dbf' (ensuring the correct order for the
>>shape-information-mapping). Or another example, render some area shapes
>>on
>>the one hand with popuplation data and on the other hand with
>>unemployment
>>data without integrating both data sets into the dbf of the shape file
>>and
>>without producing two different shape-files. I use php-mapscript and
>>mapserver 4.4.
>>
>>HolgeR
>>
>
>