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Question

Change detector on attributes only

  • February 12, 2018
  • 7 replies
  • 94 views
J
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Hi everyone,

I'm trying to compare 2 PostGIS spatial table (points representing airports) to detect changes. When there's a change in geometry, the change detector works great. But when there's a change only on an attribute in a raw, I can't find it!

In fact I can find it if I select the right field name in the parameters (because I know wich field has been changed in my test). But it doesn't work when I select all attributes, which is the real situation. I need to detect changes on tables with unknown atrributes updates. Match geometry is always set to "none" in this case beacuse I want to check changes only on attributes.

I've also tried to combine CRCcalculator, feature merger, update detector, tester, etc. but even for a very simple test - only one non-geometric attribute in a raw changed between the 2 tables - I can't find a way to make this change appear in a transformer output...

Any help would be very appreciated

Thanks!

7 replies

J
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By attribute I mean a value in a field, not the field name itself... Sorry for this translation issue

david_r
Evangelist
  • david_rEvangelist
  • February 13, 2018

Could it be that the transformer has an issue with binary attribute values? Try inserting a PythonCaller with the following code just before the ChangeDetector:

from fmeobjects import *
 
def ConvertBinaryToHex(feature):
    for attr in feature.getAllAttributeNames():
        attr_value = feature.getAttribute(attr)
        if isinstance(attr_value, bytearray):
            # Convert bytearray to string with hexadecimal values
            hex_value = ''.join('{:02x}'.format(x) for x in attr_value)
            feature.setAttribute(attr, hex_value)

This will convert all the binary attribute values to hexadecimal strings. 

J
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Hi David, thanks a lot for your help. The script seems to work but the value of my new "hex_value" field is <missing>... I think I set properly the parameters of the python caller since I can add and see other extra field with a simple string value (as a test since I'm not a python specialist).

I have entirely empty and <null> fields in my table. Could it be an issue ?

david_r
Evangelist
  • david_rEvangelist
  • February 13, 2018
jeremielemarcha wrote:

Hi David, thanks a lot for your help. The script seems to work but the value of my new "hex_value" field is <missing>... I think I set properly the parameters of the python caller since I can add and see other extra field with a simple string value (as a test since I'm not a python specialist).

I have entirely empty and <null> fields in my table. Could it be an issue ?

I'm not sure I understand. Could you post some screenshots?
J
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david_r wrote:
I'm not sure I understand. Could you post some screenshots?
Yes sure. Here you can see the hex_value field stays <missing>

 

J
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jeremielemarcha wrote:
Yes sure. Here you can see the hex_value field stays <missing>

 

I tried the change detector alone in a blank workspace and now it detects the only value that has change between my two PostGIS tables. I don't know why it works now...

 

 

If you have any information about the <missing> hex_value field, I'm still interested to understand

 

 

Anyway, thanks a lot for your help !

 

 

david_r
Evangelist
  • david_rEvangelist
  • February 13, 2018
jeremielemarcha wrote:
Yes sure. Here you can see the hex_value field stays <missing>

 

Unless there's an attribute called "hex_value" on your feature before the PythonCaller, there won't be one after the PythonCaller either. The PythconCaller "re-codes" all the binary values in place, i.e. on the same attribute name.

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