How do you change an item's category/give it one?

[mimib14]

There's something from a mod I want to use, but I can't store it anywhere because it doesn't seem to have any category, so I can't enable or disable it in any stockpiles. How do I set an item's category (like Meals, Raw Resources, Weapons, etc etc)?

[joaonunes]

Through the defs files. Check other already existing mods that add items and see how they are defining the items

[1000101]

You need to assign at least one ThingCategoryDef (thingCategories) to the ThingDef.

[jacob814]

The best way I figured this out is to look at a file in the core folder like the building_furniture. The bed is in a few thingCategories.