code: public void putSingleEntity(String keyName) {
      // [START putSingleEntity]
      Key key = datastore.newKeyFactory().setKind("MyKind").newKey(keyName);
      Entity.Builder entityBuilder = Entity.newBuilder(key);
      entityBuilder.set("propertyName", "value");
      Entity entity = entityBuilder.build();
      datastore.put(entity);
      // [END putSingleEntity]
    }
docs: [VARIABLE "my_key_name"]