# Item Query

The ItemQuery system is a separate module (Just like how the crafting system is a separate module) that includes a system that allows for quickly filtering and querying a specific set of items while supporting multithreading.

These queries are very simple; They listen to specific events and if they pass the filtering function, they are added to an array, which can be reused extremely efficiently.

To enable item querying, add the AC_ItemQueryManager component to your actor.

To add a ItemQuery to the manager, either add one to the ItemQueries array inside the component, or call ConstructObjectFromClass (We use this function so any ExposeOnSpawn parameters can be set) or use NewObject<>() if you're in C++, and then call AC_ItemQueryManager -> RegisterItemQuery

To then get the items from the query, you can either call AC_ItemQueryManager -> GetItemsFromQueryByClass/GetItemsFromQueryByIdentifier or call GetItemsFromQuery on the item query instance you just created.

The ItemQuery is now responsible for listening to any events relevant to it. For example, if you wanted to filter out all items with a specific tag, you would listen to the ItemTagAdded/ItemTagRemoved delegate. If an item had the tag added, you'd register the item. If the item had the tag removed, you're unregister the item.
By default, all queries will automatically listen to 4 delegates:

ComponentStarted - It will try to register all items.
ComponentStopped - All items will now be removed from the query.
ItemAdded - It will try to register a newly added item
ItemRemoved - It will remove the item from the query.

# Creating a query

To create a ItemQuery:

Right click the content browser and select InventoryFramework -> Other -> ItemQuery
Override the QueryRegistered function and bind the relevent delegates your query will use. Then call RegisterItem and UnregisterItem when needed.
Override the DoesItemPassFilter to dictate what items will ultimately get registered with the query.

The example project includes 2 examples.

# Performance

In a test of over 300 items, registering a query that checked for a tag on the item took on average 500 microseconds, which is only 1/32 of a 60 FPS frame budget. Getting those items from the query then took on average 100 microseconds.

For maximum performance, it's recommended to remove the BlueprintNativeEvent from the DoesItemPassFilter function and only use C++ item queries. As talked about in the Optimizations page, removing Blueprint support can improve performance by about 16 times.
The main area that C++ dominates Blueprints are heavy for-loops. In this test, running a similar hard-coded query through blueprint code took a whopping 34.7 milliseconds. These queries provide a simple interface for blueprint programmers to leverage the speed of C++ while staying in Blueprints by just overriding one function.
The only downside for queries in regards to performance is that they take up memory, but it shouldn't be that much that you'd notice.
Queries can be multithreaded. This can be extremely powerful in the right scenarios. For example, spawning the equipment can be expensive. This is why the manager component will try to multithread its default queries while that is happening, greatly improving CPU utilization.
- Do keep in mind that sending a task to a different thread does have a small cost. I advise you to use Unreal Insights to evaluate whether it is worth for your inventory to bother with multithreading or not

Keep in mind, Blueprint debugger does not work when blueprint code is NOT being executed on the game thread. So blueprint breakpoints won't work in the multithreading scenario

# Storing extra information

Queries do not just have to store a list of items. Since queries are living objects, you can store whatever information you want.
The example project includes a query that keeps track of specific item asset and how many of that item asset there are.