Build Arcpy Field Mapping Object from Table

MicahBabinski

Does anyone know if it is possible to store information on input datasets, input fields, and destination fields in a table, and then use arcpy to build a field mapping object from said table? I have built arcpy field mapping objects in the past using blocks of code for each field, but don't have any experience reading the info out of a table and building the table using an iterator.

I'd love to get your thoughts!

Warm Regards,

Micah Babinski

MicahBabinski

Thank you all very much for your input! In the end I only needed a table with three fields:

From there I wrote the following script (as it would be implemented in a script tool):

<SPAN class="comment token"># Name: appendWithFieldMap.py</SPAN>
<SPAN class="comment token"># Author: Micah Babinski</SPAN>
<SPAN class="comment token"># Date: 9/8/2016</SPAN>
<SPAN class="comment token"># Description: Appends features to an output feature class using field mapping information stored in a table</SPAN>
<SPAN class="comment token">#</SPAN>
<SPAN class="comment token"># USAGE NOTE: The table must contain three columns</SPAN>
<SPAN class="comment token">#&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 1. SourceTablepath (fully-qualified path to the source feature class</SPAN>
<SPAN class="comment token">#&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 2. SourceFieldName (name of the input field as it appears in the source feature class</SPAN>
<SPAN class="comment token">#&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 3. DestinationFieldName (destination field name as it appears in the destination feature class)</SPAN>

<SPAN class="keyword token">import</SPAN> arcpy
<SPAN class="keyword token">import</SPAN> sys

<SPAN class="comment token"># obtain user parameters</SPAN>
outputFeatureClass <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>GetParameterAsText<SPAN class="punctuation token">(</SPAN><SPAN class="number token">0</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="comment token">#r"W:\FieldMappingResearch\gdb\Output.gdb\roads"</SPAN>
fieldMapTable <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>GetParameterAsText<SPAN class="punctuation token">(</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="comment token">#r"W:\FieldMappingResearch\gdb\Inputs.gdb\fieldMapTable"</SPAN>

<SPAN class="comment token"># list the fields which contain the field map info</SPAN>
fields <SPAN class="operator token">=</SPAN> <SPAN class="punctuation token">[</SPAN><SPAN class="string token">"SourceTablePath"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"SourceFieldname"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"DestinationFieldName"</SPAN><SPAN class="punctuation token">]</SPAN>

<SPAN class="comment token"># define function to get unique field values from a table</SPAN>
<SPAN class="keyword token">def</SPAN> <SPAN class="token function">GetUniqueFieldValues</SPAN><SPAN class="punctuation token">(</SPAN>table<SPAN class="punctuation token">,</SPAN> field<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="string token">"""
&nbsp;&nbsp;&nbsp; Retrieves and prints a list of unique values in a user-specified field

&nbsp;&nbsp;&nbsp; Args:
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; table (str): path or name of a feature class, layer, table, or table view
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; field (str): name of the field for which the user wants unique values

&nbsp;&nbsp;&nbsp; Returns:
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; uniqueValues (list): a list of the unique values in the field
&nbsp;&nbsp;&nbsp; """</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="comment token"># get the values</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">with</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>da<SPAN class="punctuation token">.</SPAN>SearchCursor<SPAN class="punctuation token">(</SPAN>table<SPAN class="punctuation token">,</SPAN> <SPAN class="punctuation token">[</SPAN>field<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="keyword token">as</SPAN> cursor<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> sorted<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">{</SPAN>row<SPAN class="punctuation token">[</SPAN><SPAN class="number token">0</SPAN><SPAN class="punctuation token">]</SPAN> <SPAN class="keyword token">for</SPAN> row <SPAN class="keyword token">in</SPAN> cursor<SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN>

<SPAN class="comment token"># get a list of unique input feature classes</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Listing the unique input feature classes."</SPAN><SPAN class="punctuation token">)</SPAN>
inputs <SPAN class="operator token">=</SPAN> GetUniqueFieldValues<SPAN class="punctuation token">(</SPAN>fieldMapTable<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"SourceTablePath"</SPAN><SPAN class="punctuation token">)</SPAN>

<SPAN class="comment token"># get a list of unique output fields</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Listing the unique output fields."</SPAN><SPAN class="punctuation token">)</SPAN>
outputFields <SPAN class="operator token">=</SPAN> GetUniqueFieldValues<SPAN class="punctuation token">(</SPAN>fieldMapTable<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"DestinationFieldName"</SPAN><SPAN class="punctuation token">)</SPAN>

<SPAN class="comment token"># create an empty field mappings object</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Creating an empty field mappings object."</SPAN><SPAN class="punctuation token">)</SPAN>
fm <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>FieldMappings<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>

<SPAN class="comment token"># build the field mappings object</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Building the field mappings object."</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="keyword token">for</SPAN> f <SPAN class="keyword token">in</SPAN> outputFields<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"\t"</SPAN> <SPAN class="operator token">+</SPAN> f <SPAN class="operator token">+</SPAN> <SPAN class="string token">"..."</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="comment token"># create a field map object</SPAN>
&nbsp;&nbsp;&nbsp; arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"\t...Creating a field map object."</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; fMap <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>FieldMap<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">with</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>da<SPAN class="punctuation token">.</SPAN>SearchCursor<SPAN class="punctuation token">(</SPAN>fieldMapTable<SPAN class="punctuation token">,</SPAN> fields<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"""{0} = '{1}'"""</SPAN><SPAN class="punctuation token">.</SPAN>format<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"DestinationFieldName"</SPAN><SPAN class="punctuation token">,</SPAN> f<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="keyword token">as</SPAN> cursor<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">for</SPAN> row <SPAN class="keyword token">in</SPAN> cursor<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="comment token"># add the input field to the field map</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"\t...Adding "</SPAN> <SPAN class="operator token">+</SPAN> row<SPAN class="punctuation token">[</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN> <SPAN class="operator token">+</SPAN> <SPAN class="string token">" as an input field."</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; fMap<SPAN class="punctuation token">.</SPAN>addInputField<SPAN class="punctuation token">(</SPAN>row<SPAN class="punctuation token">[</SPAN><SPAN class="number token">0</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">,</SPAN> row<SPAN class="punctuation token">[</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="comment token"># set the output name</SPAN>
&nbsp;&nbsp;&nbsp; arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"\t...Setting the output name."</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; outputFieldName <SPAN class="operator token">=</SPAN> fMap<SPAN class="punctuation token">.</SPAN>outputField
&nbsp;&nbsp;&nbsp; outputFieldName<SPAN class="punctuation token">.</SPAN>name <SPAN class="operator token">=</SPAN> f
&nbsp;&nbsp;&nbsp; fMap<SPAN class="punctuation token">.</SPAN>outputField <SPAN class="operator token">=</SPAN> outputFieldName
&nbsp;&nbsp;&nbsp; 
&nbsp;&nbsp;&nbsp; <SPAN class="comment token"># add the field map to the field mappings object</SPAN>
&nbsp;&nbsp;&nbsp; arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"\t...Adding the field map to the field mappings object."</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; fm<SPAN class="punctuation token">.</SPAN>addFieldMap<SPAN class="punctuation token">(</SPAN>fMap<SPAN class="punctuation token">)</SPAN>

<SPAN class="comment token"># perform the append</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>AddMessage<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"\nAppending!"</SPAN><SPAN class="punctuation token">)</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>Append_management<SPAN class="punctuation token">(</SPAN>inputs<SPAN class="punctuation token">,</SPAN> outputFeatureClass<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"NO_TEST"</SPAN><SPAN class="punctuation token">,</SPAN> fm<SPAN class="punctuation token">)</SPAN>
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

To summarize, the workflow was:

1. Obtain a unique list of input feature classes (full paths, for use in the append GP tool)
2. Obtain a unique list of the output fields (one arcpy.FieldMap() object is needed per output field)
3. Create an empty field mappings object
4. For each output field, create an empty field map object, obtain the input fields for that output field with a da.SearchCursor, add those to the field map object, set the name of the output field, and add the field map to the field mappings object

I imagine that there is a lot more that could be done with this in terms of validation and error handling (for when field types are mismatched) but I think this will get me what I need.

Thanks again!

Micah