David Weiss David Weiss - 1 month ago 19
Swift Question

With Realm, should I use a List object or Results object as the data source for a UITableView?

There are at least 2 main collection types used in Realm:


  1. List

  2. Results



The relevant description from the documentation on a
Results
object says:


Results is an auto-updating container type in Realm returned from
object queries.


Because I want my
UITableView
to respond to any changes on the Realm Object Server, I really think I want my
UITableView
to be backed by a
Results
object. In fact, I think I would always want a
Results
object to back my UI for this reason. This is only reinforced by the description of a
List
object in the documentation:


List is the container type in Realm used to define to-many
relationships.


Sure seems like a
List
is focused on data modeling... So, being new to Realm and just reading the API, I'm thinking the answer is to use the
Results
object, but the tutorial (Step 5) uses the
List
object while the RealmExamples sample code uses
Results
.

What am I missing? Should I be using
List
objects to back my
UITableViews
? If so, what are the reasons?

Answer

Short answer: use a List if one already exists that closely matches what you want to display in your table view, otherwise use a Results.

If the data represented by a List that's already stored in your Realm corresponds to what you want to display in your table view, you should certainly use that to back it. Lists have an interesting property in that they are implicitly ordered, which can sometimes be helpful, like in the tutorial you linked to above, where a user can reorder tasks.

Results contain the results of a query in Realm. Running this query typically has a higher runtime overhead than accessing a List, by how much depends on the complexity of the query and the number of items in the Realm.

That being said, mutating a List has performance implications too since it's writing to the file in an atomic fashion. So if this is something that will be changing frequently, a Results is likely a better fit.