Archetype/app/services/archetypeCacheService.js

angular.module('umbraco.services').factory('archetypeCacheService', function (archetypePropertyEditorResource) {
    //private

    var isEntityLookupLoading = false;
    var entityCache = [];
    var isDatatypeLookupLoading = false;
    var datatypeCache = [];

    return {
		getDatatypeByGuid: function(guid) {
        	var cachedDatatype = _.find(datatypeCache, function (dt){
	            return dt.dataTypeGuid == guid;
	        });

	        if(cachedDatatype) {
	            return cachedDatatype;
	        }

	        //go get it from server
	        if (!isDatatypeLookupLoading) {
	            isDatatypeLookupLoading = true;

	            archetypePropertyEditorResource.getDataType(guid).then(function(datatype) {

	            	datatype.dataTypeGuid = guid;

	                datatypeCache.push(datatype);

	                isDatatypeLookupLoading = false;

	                return datatype;
	            });
	        }

	        return null;
        },
     	getEntityById: function(scope, id, type) {
	        var cachedEntity = _.find(entityCache, function (e){
	            return e.id == id;
	        });

	        if(cachedEntity) {
	            return cachedEntity;
	        }

	        //go get it from server
	        if (!isEntityLookupLoading) {
	            isEntityLookupLoading = true;

	            scope.resources.entityResource.getById(id, type).then(function(entity) {

	                entityCache.push(entity);

	                isEntityLookupLoading = false;

	                return entity;
	            });
	        }

	        return null;
	    }
    }
});