Set default value for a field in ArcMap using python

[StacyMcNeil]

I have been trying to figure out how I can set a default value to a field in ArcMap.  I see there is a tool called Assign Default to field but that is applied to the entire dataset.  I would like the default to apply to the current ArcMap session only.  In the Create Features window you can right click a layer and set a default there to get the behavior I would like but am trying to accomplish this for multiple layers in the TOC using python.

This is what I have been trying, starting with one layer first, but get an error "The attribute 'defaultValue' is not supported on this instance of Field"  I can print the defaultValue however.

feature_class = "Roads"

fields = arcpy.ListFields(feature_class)

for field in fields:

     if field.name == "Project_Name":

          field.defaultValue = "Test_Project"

Forgive me if I am making an obvious mistake.  I am still a beginner.  Thanks for any help!

[SepheFox]

import os   

import arcpy 

def AssignDefault(tbl, fld):   

     try:   

          fname = arcpy.ListFields(tbl, fld)[0].name   

          mxd = arcpy.mapping.MapDocument("CURRENT")   

          default = os.path.splitext(arcpy.Describe(mxd.filePath).name)[0]   

          arcpy.AssignDefaultToField_management(tbl, fname, default) 

          print default 

     except:   

          print("Could not assign default")

AssignDefault("Roads", "Project_Name")

[StacyMcNeil]

Thanks Dan.  I haven't used functions much.  I did get it to run but as I thought, the default value was assigned to the feature class itself so when I go to another map the same default value is present.  That is why I was trying to use the defaultValue property for the field.  What I really need is a default on a field that will exist for in the mxd only.  Just like how you can set it in the template properties when creating a new feature.  Maybe this is not possible.

[curtvprice]

No, it isn't possible because that default value is a property of the data, not an mxd which points to it.

[JeffWard]

Have you looked at the Attribute Assistant?  It allows you to establish a default value for a field.

You need to have a table called DynamicValue added to your map.

The Attribute Assistant has a method called EXPRESSION that would allow you to put a value in a field.

I actually just tested this on a feature class called Roads with a text field of Project_Name.  The entry in the DynamicValue table looks like this

I don't think there's a place you can download the Attribute Assistant by itself.  It comes packaged with the Local Government map templates in the maps and apps folder that comes with the bundle.  You can download the Address Management template here, open up the template and look at their DynamicValue table to see how it is configured.

[StacyMcNeil]

Thanks Jeff.  I will look at that.  Thanks to all others who tried to help me!  Just to be sure,before I give up, there is no way to access the Create Feature Template Properties with python and I cannot use field.defaultValue to assign a default?  Many thanks!

[NilsBabel]

Hi Stacy, did you ever find a solution to this?  I'm trying to do something very similar.  Seems like you'd have to access the edit features template to change the default value only in the map document.  I haven't found a way to do that in ArcPy. 

[StacyMcNeil]

Hi Nils.  Sorry it took me so long to answer you.  There is no way to do this with ArcPy. I had to learn some ArcObjects to accomplish this.  You can set a default value through the layer extensions (ILayerExtension) and then access the template manager (IEditTemplateManager) and edit the template (IEditTemplate).  One problem I ran into that is now logged as a bug is that you have to start an edit session for this to work.  If you would like some sample code let me know.

[AndrewQuee]

Hi Stacy, we're looking at a very similar job to your original post.  Could you please post your sample code?  If it's too long Pastebin.com  would be fine.

[StacyMcNeil]

Hi Andrew.  Just seeing this now.  Here it is.  I was hoping to do this outside of ArcMap but found that you have to start an editing session to get it to work so created it as an Add-In.  I  have reported this to ESRI as a bug but don't think it has been fixed yet.

    Protected Overrides Sub OnClick()
        Dim ipDoc As ESRI.ArcGIS.ArcMapUI.IMxDocument 'ArcMapUI
        ipDoc = CType(My.ArcMap.Application.Document, ESRI.ArcGIS.ArcMapUI.IMxDocument)
        Dim pMap As ESRI.ArcGIS.Carto.IMap
        pMap = ipDoc.FocusMap
        Dim pDocInfo As IDocumentInfo2 = CType(ipDoc, IDocumentInfo2)
        Dim pEnumLayer As IEnumLayer
        Dim pLayer As ILayer
        Dim pFeatureLayer As IFeatureLayer
        Dim pFeatureClass As IFeatureClass
        Dim pDataset As IDataset
        Dim Plan_Num As String
        Dim idx As Integer
        Dim m_editor As IEditor
        Dim editorUid As New UID()
        editorUid.Value = "esriEditor.Editor"
        m_editor = TryCast(My.ArcMap.Application.FindExtensionByCLSID(editorUid), IEditor)

        'Gets numbers from the name of the map which is the Plan_Num and will be used to set default values
        Plan_Num = Integer.Parse(Regex.Replace(pDocInfo.Name, "[^\d]", ""))


        pEnumLayer = pMap.Layers(Nothing, True)
        pEnumLayer.Reset()
        pLayer = pEnumLayer.Next

        For idx = 0 To pMap.LayerCount - 1
            Do Until pLayer Is Nothing
                If TypeOf pLayer Is IFeatureLayer2 And Not TypeOf pLayer Is RasterLayer Then
                    Try
                        pFeatureLayer = pLayer
                        pFeatureClass = pFeatureLayer.FeatureClass
                        If Not pFeatureClass.FeatureDataset Is Nothing Then
                            pDataset = pFeatureClass.FeatureDataset
                            'Loop through layers in the Plans feature dataset and set default value for Plan_Num
                            If pDataset.Name = "REF.SDE.Plans" Then
                                Dim pWorkSpace As IWorkspace = pDataset.Workspace
                                Dim pWorkEdit As IWorkspaceEdit = pWorkSpace
                                If pWorkEdit.IsBeingEdited = False Then
                                    'Start an edit session
                                    m_editor.StartEditing(pDataset.Workspace)
                                    pFeatureLayer = pLayer
                                    Dim pLayerExt As ESRI.ArcGIS.Carto.ILayerExtensions
                                    pLayerExt = CType(pFeatureLayer, ESRI.ArcGIS.Carto.ILayerExtensions)
                                    Dim jdx As Integer
                                    For jdx = 0 To pLayerExt.ExtensionCount - 1
                                        Dim obj As Object = pLayerExt.Extension(jdx)
                                        If TypeOf obj Is ESRI.ArcGIS.Carto.IEditTemplateManager Then
                                            Dim pEditTemplateMgr As ESRI.ArcGIS.Carto.IEditTemplateManager
                                            pEditTemplateMgr = CType(obj, ESRI.ArcGIS.Carto.IEditTemplateManager)
                                            Dim pEditTemplate As IEditTemplate = pEditTemplateMgr.EditTemplate(jdx)
                                            Dim kdx As Integer
                                            For kdx = 0 To pEditTemplateMgr.Count - 1
                                                pEditTemplateMgr.EditTemplate(kdx).SetDefaultValue("Plan_num", Plan_Num, True)
                                            Next
                                        End If
                                    Next
                                    m_editor.StopEditing(False)
                                Else
                                    MsgBox("Please stop editing and try to run tool again")
                                End If
                            End If
                        End If
                    Catch ex As Exception
                        MsgBox("Error! Default value not set for " + pLayer.Name)
                    End Try
                        End If
                pLayer = pEnumLayer.Next
            Loop
        Next
        My.ArcMap.Application.SaveDocument()
        MsgBox("Process complete. Map can be closed.")
        My.ArcMap.Application.CurrentTool = Nothing
    End Sub‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍