mjhjmtu

I've deployed 2 versions of a custom xConnect model I created called DetailModel.

According to the documentation, the xConnect models' unique name is name of model + version.

The model’s full name (represented by the FullName property of the
XdbModel class) includes the model’s name and version. For example:
DocumentationModel,1.0.

Described here: https://doc.sitecore.com/developers/90/sitecore-experience-platform/en/create-a-model.html

I have deployed both models:

• DetailModel, 0.1.json


• DetailModel, 0.2.json

But I get an error in xConnect and the IndexWorker regarding: different models with the same names are referenced.

2019-03-11 12:08:56.970 +01:00 [Error] Exception occurred during instantiating of IndexerHost.
Sitecore.XConnect.Schema.DuplicateXdbModelNameException: Different models with the same names are referenced ('DetailModel')
 at Sitecore.XConnect.Schema.XdbModel.AddAndValidateModelAndTypes(XdbModel model, HashSet`1 visited)
 at Sitecore.XConnect.Schema.XdbModel.AddAndValidateModelAndTypes(XdbModel model, HashSet`1 visited)
 at Sitecore.XConnect.Schema.XdbModel..ctor(String name, XdbModelVersion version, XdbNamedType types, XdbFacetDefinition facets, XdbModel referencedModels)
 at Sitecore.XConnect.Schema.XdbRuntimeModel..ctor(XdbModel models)
 at Sitecore.XConnect.Search.Indexer.Extensions.UseXConnectModel(IServiceCollection services, DirectoryInfo modelsPath)
 at Sitecore.XConnect.Search.Indexer.IndexerHost.GetDiServiceProvider(IConfiguration config, String modelDirectory, EventHandler configOrModelChangedHandler)
 at Sitecore.XConnect.Search.Indexer.IndexerHost..ctor(IConfigurationRoot config)
 at Sitecore.XConnect.Search.Indexer.IndexerAppDomainHost.IndexerHostAppDomainBridge..ctor()

Why am I getting this error? I would assume that it is possible to have multiple versions deployed.

Even though it seems confusing at first, but different XConnect model version does not make model unique only model name does. Model versions can be used for your own sake to keep track of different model versions. However, XConnect cannot handle two or more versions of the same model.
On a related note, all referenced models have to have unique names as well (see the last section in Sitecore documentation:

Model names must be unique across all referenced models, including second order references. For example:

A model named CRM.Model cannot reference another model named CRM.Model

A model named CRM.Model cannot reference Documentation.Model which in turn references another model named CRM.Model

A DuplicateModelNameException exception is thrown if model names are not unique.