Player Inventory

The inventory screen is the workhorse for filters, joins and atomic writes: items a player owns, queried by owner, kept consistent as items are granted or consumed.

note

This example shares its InventorySlot schema and GrantItem command with the Build Your First Game tutorial, which introduces and explains them. Keep the two in sync if you change either.

Schema

table InventorySlot(plural: InventorySlots, persistence: local, capacity: 4096, type_id: 2) {
    Id: int @id
    PlayerId: int
    ItemId: int
    Amount: int

    @@unique(fields: [PlayerId, ItemId], name: "InventorySlot_Player_Item")
}

The @@unique(PlayerId, ItemId) constraint guarantees at most one slot per (PlayerId, ItemId) and accelerates exact full-pair lookups. It does not accelerate the per-player GetInventory query, which binds only the leading PlayerId column — a unique index is a full-key hash probe with no partial-key/prefix capability, so that filter would full-scan. To make per-player lookups fast, add a dedicated leading-column index: @@index(fields: [PlayerId], kind: lookup) (a multi-value hash returning all of a player's slots).

Query

query GetInventory(playerId: int) -> InventorySlot[] {
    from InventorySlots
    | filter PlayerId == @playerId
    | sort ItemId
}

Mutate atomically with a command

Granting an item is a single, atomic state transition — an upsert that accumulates the amount, with a guard that rejects invalid input at compile-checked boundaries:

module Inventory {
    command GrantItem(playerId: int, itemId: int, amount: int) -> GrantItemResult
    kind local
    {
        require amount > 0 else InvalidAmount

        upsert InventorySlots
        | key { PlayerId: playerId, ItemId: itemId }
        | set Amount += amount
        | returning { amountAfter: Amount } into slotAfter

        return {
            itemId: itemId,
            amountAfter: slotAfter.amountAfter
        }
    }
}

Call it from C#

using ConjureDB;

using var ctx = DbContextBuilder<GameDbContext>.Create()
    .WithDataDirectory("./data")
    .WithDefaultSnapshot()
    .Build();

var slots = ctx.GetInventory(playerId: 1);

Validation failures (here, InvalidAmount) are modelled as typed command outcomes, not exceptions — see Getting Started for the full command workflow.