3079: "Domain already exists" in Collector for ArcGIS

Error Message

When loading a map in Collector, “Error 3079: Domain already exists” may be encountered in the Layers tool, and the layer with the error doesn’t load in Collector.

“Error 3079: Domain already exists” 

Cause

This error occurs if using a hosted feature layer in ArcGIS Online and any of the following applies:

• It was created in ArcGIS Online (for example, from a template or existing feature layer) before the 7.1 update (March 2019) and all the following applies for the hosted feature layer:
  • It contains multiple layers.
  • Two or more of the layers have fields with the same name but different lists (domains), and the lists were created or edited in ArcGIS Online.

For example, you create a hosted feature layer of park information, including a paths (lines) layer and an areas (polygons) layer. In this example layer, the paths and areas layers each have a field “surface_type” with a list (domain). Paths can have a surface type of paved, dirt, or gravel, while areas can be paved, grass, dirt, gravel, or sand. The list (domain) choices are different, but the field has the same name. Data with this structure that was created in ArcGIS Online before the 7.1 update (March 2019) shows the error in Collector, since the lists (domains) were given the same name but have different values.

• It was created by publishing from ArcGIS Pro or ArcMap before the 7.3 update to ArcGIS Online (October 2019) and all the following applies for the hosted feature layer:
  • The layer(s) were published from a single geodatabase.
  • The original geodatabase contained domains shared between multiple feature classes or multiple fields.
  • The shared domain was updated in ArcGIS Online so that it is no longer the same for all layers and fields.  

For example, consider a geodatabase of park information, including paths (a line feature class), areas (a polygon feature class), and a “surface_type” domain used by both feature classes. After publishing a hosted feature layer based on those feature classes, the list (domain) for the paths layer was updated to add a new value while the list for the areas layer remained unchanged. The list choices for each layer are different, but the lists have the same name since it was shared in the geodatabase. Data with this structure that was published from ArcGIS Pro or ArcMap to ArcGIS Online before the 7.3 update (October 2019) shows the error in Collector since the lists (domains) were given the same name but have different values.

• It was created by publishing from ArcGIS Pro or ArcMap and all the following applies for the hosted feature layer:
  • The layers were published from different geodatabases into a single hosted feature layer.
  • The original geodatabases contained domains of the same name but different codes and values.

For example, there are two geodatabases, one with street information and one with park information. Both have domains of “surface_type”, but the choices for the domains are different, as one contains street surfaces and other contains park surfaces. A street feature class using the street “surface_type” domain and a park feature class using the park “surface_type” domain were published from ArcGIS Pro or ArcMap to a single hosted feature layer. The list (domain) choices for the street and park layers are different, but the lists have the same name since it was the same in both geodatabases. Data with this structure that was published from ArcGIS Pro or ArcMap to ArcGIS Online before the 7.3 update (October 2019) shows the error in Collector since the lists (domains) were given the same name but have different values.

Solution or Workaround

Edit the domains in ArcGIS Online and re-save them to update the list (domain) names according to the updated domain naming convention. The updated domain naming convention was introduced for feature layers created in ArcGIS Online in the 7.1 update (March 2019), and for feature layers published from ArcGIS Pro or ArcMap in the 7.3 update (October 2019). The updated names are unique, the error goes away, and the layer loads. See Edit a list of values.

Alternate solution
For layers matching the third case above, where they were published from different geodatabases into a single hosted feature layer, you can also choose one of the following ways to address the issue:

1. Update the domain names in the geodatabases so that they are unique and republish the layer.
2. Publish each layer to ArcGIS Online as a separate hosted feature layer (instead of publishing a single hosted feature layer with both layers in it).

Note:
This error may also occur if a list was updated in ArcGIS Online while the map with the layer was open in Collector. In that case, when the user who had the map open reloads the map, they’ll see this error. To fix this case, close the app and reopen it.