SwiftData lazy loaded list

Question

magnuti OP

Created 6d

Replies 1

Boosts 1

Participants 2

Are SwiftData queries lazy loaded when used in conjunction with SwiftUI List?

@Query
var posts: [PostModel]

List {
    ForEach(posts, id: \.id) { post in
        PostView(post)
    }
}

If the code above is not lazy loaded, how can we make it lazy loaded?

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Answer 1

mahaoyu OP

5d

Hi, I would be curious about this as well.

I'm not a 100% sure, but I think while the List itself builds lazily, the underlying Query executes fully and loads into memory. My suspicion comes from empirical observation constructing a test case similar to your posts example - using a chunky dataset and displaying that in a List with high debug output (using flag -com.apple.CoreData.SQLDebug 3) the logs would indicate a full load of the underlying entity into memory.

In my example I'm dabbling with a dictionary of ~120k entries and .searchable list. I'm creating a dynamic filter through a subview using the @Query macro. W/o debouncing it or anything similar, this freezes the UI on every key stroke, as I believe it does the full load just like below every single time...

CoreData: annotation: Connecting to sqlite database file at ...
CoreData: sql: SELECT TBL_NAME FROM SQLITE_MASTER WHERE TBL_NAME = 'Z_METADATA'
CoreData: sql: pragma recursive_triggers=1
CoreData: sql: pragma journal_mode=wal
...
CoreData: annotation: sql connection fetch time: 0.1419s
CoreData: annotation: fetch using NSSQLiteStatement <0x600002c5d040> on entity 'DictionaryItem' with sql text 'SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZDEFINITION, t0.ZPINYIN, t0.ZSC, t0.ZTC FROM ZDICTIONARYITEM t0 WHERE (CASE (? = ?) when 1 then (?) else ((CASE (( NSCoreDataStringSearch( t0.ZSC, ?, 417, 1) OR  NSCoreDataStringSearch( t0.ZDEFINITION, ?, 417, 1))) when 1 then (?) else (?) end)) end) = ? ORDER BY t0.Z_PK' returned 122780 rows
CoreData: annotation:  with values: (
    "<NSManagedObject: 0x600002c7e0d0> (entity: DictionaryItem; id: 0x90a265083a343fde <x-coredata://F80EEF97-F2E4-46EE-84DC-FB33BFB0AA0B/DictionaryItem/p1>; data: <fault>)",
    "<NSManagedObject: 0x600002c7df40> (entity: DictionaryItem; id: 0x90a265083a543fde <x-coredata://F80EEF97-F2E4-46EE-84DC-FB33BFB0AA0B/DictionaryItem/p2>; data: <fault>)",
    "<NSManagedObject: 0x600002c7e3a0> (entity: DictionaryItem; id: 0x90a265083a743fde <x-coredata://F80EEF97-F2E4-46EE-84DC-FB33BFB0AA0B/DictionaryItem/p3>; data: <fault>)”,
…
26533c9543fde <x-coredata://F80EEF97-F2E4-46EE-84DC-FB33BFB0AA0B/DictionaryItem/p122778>; data: <fault>)",
    "<NSManagedObject: 0x60000acbf6b0> (entity: DictionaryItem; id: 0x90a26533c9743fde <x-coredata://F80EEF97-F2E4-46EE-84DC-FB33BFB0AA0B/DictionaryItem/p122779>; data: <fault>)",
    "<NSManagedObject: 0x60000acbf700> (entity: DictionaryItem; id: 0x90a26533c9943fde <x-coredata://F80EEF97-F2E4-46EE-84DC-FB33BFB0AA0B/DictionaryItem/p122780>; data: <fault>)"
)
CoreData: annotation: total fetch execution time: 6.7316s for 122780 rows.
…

(Repeats for every keystroke, e.g. typing ‘apple’ incrementally narrows down the result set but the first few strokes are large chunks just like the full dictionary)

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