[1.15.2] Adding drops to mobs

[DeJunky]

I just started out learning forge modding so I'm creating a simple mod that adds an extra crop to the game. I would like to add a chance for zombies to drop the seed item for this crop and I'm not sure how to go about this.

Basically, how can I add my item to the loot table for zombies, or how could I inject my item into the loot table?

Edited June 4, 2020 by DeJunky
Update title

[Draco18s]

Global Loot Modifiers

https://github.com/MinecraftForge/Documentation/blob/c07a887ab55063073494c8c5b99bcb599fea23c9/docs/items/globallootmodifiers.md

[DeJunky]

First of all, thanks for the help and the link to some great documentation. Perhaps it's just my lack of knowledge about loot tables but I was running into trouble trying to get a mob to drop the item. I was able to code up a condition for it to drop from a block and it worked just fine, however when I play test with this loot modifier

{
  "type":"onion:add_onion",
  "conditions": [
    {
      "condition": "minecraft:entity_properties",
      "entity": "this",
      "predicate": {
        "type": "minecraft:zombie"
      }
    }
  ]
}

 

I get a crash several seconds after loading into a world. I suspect that the issue is with the way I've written the conditions as it seems to be overloading checking entities(I'm guessing).

Here is a crash report.

[20:37:06] [Server thread/INFO] [minecraft/MinecraftServer]: Stopping server
[20:37:06] [Server thread/INFO] [minecraft/MinecraftServer]: Saving players
[20:37:06] [Render thread/INFO] [STDOUT/]: [net.minecraft.util.registry.Bootstrap:printToSYSOUT:103]: ---- Minecraft Crash Report ----
// Why did you do that?

Time: 6/3/20 8:37 PM
Description: Exception while updating neighbours

java.lang.NullPointerException: Exception while updating neighbours
	at net.minecraft.world.storage.loot.conditions.EntityHasProperty.test(SourceFile:35) ~[?:?] {re:classloading}
	at net.minecraft.world.storage.loot.conditions.EntityHasProperty.test(SourceFile:19) ~[?:?] {re:classloading}
	at net.minecraftforge.common.loot.LootModifier.apply(LootModifier.java:53) ~[?:?] {re:classloading}
	at net.minecraftforge.common.ForgeHooks.modifyLoot(ForgeHooks.java:1194) ~[?:?] {re:classloading}
	at net.minecraft.world.storage.loot.LootTable.generate(LootTable.java:86) ~[?:?] {re:classloading}
	at net.minecraft.block.Block.getDrops(Block.java:517) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.block.BlockState.getDrops(BlockState.java:265) ~[?:?] {re:classloading}
	at net.minecraft.block.Block.getDrops(Block.java:523) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.block.Block.spawnDrops(Block.java:533) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.block.AbstractRailBlock.neighborChanged(AbstractRailBlock.java:88) ~[?:?] {re:classloading}
	at net.minecraft.block.BlockState.neighborChanged(BlockState.java:229) ~[?:?] {re:classloading}
	at net.minecraft.world.World.neighborChanged(World.java:321) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.world.World.notifyNeighborsOfStateChange(World.java:279) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.world.World.notifyNeighbors(World.java:265) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.world.World.markAndNotifyBlock(World.java:214) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.world.World.setBlockState(World.java:190) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.world.World.removeBlock(World.java:238) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.block.FireBlock.onBlockAdded(FireBlock.java:234) ~[?:?] {re:classloading}
	at net.minecraft.block.BlockState.onBlockAdded(BlockState.java:241) ~[?:?] {re:classloading}
	at net.minecraft.world.chunk.Chunk.setBlockState(Chunk.java:282) ~[?:?] {re:classloading}
	at net.minecraft.world.World.setBlockState(World.java:177) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.block.FireBlock.tryCatchFire(FireBlock.java:190) ~[?:?] {re:classloading}
	at net.minecraft.block.FireBlock.tick(FireBlock.java:131) ~[?:?] {re:classloading}
	at net.minecraft.block.BlockState.tick(BlockState.java:249) ~[?:?] {re:classloading}
	at net.minecraft.world.server.ServerWorld.tickBlock(ServerWorld.java:582) ~[?:?] {re:classloading}
	at net.minecraft.world.server.ServerTickList.tick(SourceFile:87) ~[?:?] {re:classloading}
	at net.minecraft.world.server.ServerWorld.tick(ServerWorld.java:316) ~[?:?] {re:classloading}
	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:849) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:784) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:114) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:637) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at java.lang.Thread.run(Thread.java:748) ~[?:1.8.0_191] {}


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Render thread
Stacktrace:
	at net.minecraft.world.storage.loot.conditions.EntityHasProperty.test(SourceFile:35)
	at net.minecraft.world.storage.loot.conditions.EntityHasProperty.test(SourceFile:19)
	at net.minecraftforge.common.loot.LootModifier.apply(LootModifier.java:53)
	at net.minecraftforge.common.ForgeHooks.modifyLoot(ForgeHooks.java:1194)
	at net.minecraft.world.storage.loot.LootTable.generate(LootTable.java:86)
	at net.minecraft.block.Block.getDrops(Block.java:517)
	at net.minecraft.block.BlockState.getDrops(BlockState.java:265)
	at net.minecraft.block.Block.getDrops(Block.java:523)
	at net.minecraft.block.Block.spawnDrops(Block.java:533)
	at net.minecraft.block.AbstractRailBlock.neighborChanged(AbstractRailBlock.java:88)
	at net.minecraft.block.BlockState.neighborChanged(BlockState.java:229)

-- Block being updated --
Details:
	Source block type: ID #minecraft:fire (block.minecraft.fire // net.minecraft.block.FireBlock)
	Block: Block{minecraft:rail}[shape=east_west]
	Block location: World: (-122,16,-241), Chunk: (at 6,1,15 in -8,-16; contains blocks -128,0,-256 to -113,255,-241), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at net.minecraft.world.World.neighborChanged(World.java:321)
	at net.minecraft.world.World.notifyNeighborsOfStateChange(World.java:279)
	at net.minecraft.world.World.notifyNeighbors(World.java:265)
	at net.minecraft.world.World.markAndNotifyBlock(World.java:214)
	at net.minecraft.world.World.setBlockState(World.java:190)
	at net.minecraft.world.World.removeBlock(World.java:238)
	at net.minecraft.block.FireBlock.onBlockAdded(FireBlock.java:234)
	at net.minecraft.block.BlockState.onBlockAdded(BlockState.java:241)
	at net.minecraft.world.chunk.Chunk.setBlockState(Chunk.java:282)
	at net.minecraft.world.World.setBlockState(World.java:177)
	at net.minecraft.block.FireBlock.tryCatchFire(FireBlock.java:190)
	at net.minecraft.block.FireBlock.tick(FireBlock.java:131)
	at net.minecraft.block.BlockState.tick(BlockState.java:249)
	at net.minecraft.world.server.ServerWorld.tickBlock(ServerWorld.java:582)

-- Block being ticked --
Details:
	Block location: World: (-123,15,-241), Chunk: (at 5,0,15 in -8,-16; contains blocks -128,0,-256 to -113,255,-241), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at net.minecraft.world.server.ServerTickList.tick(SourceFile:87)
	at net.minecraft.world.server.ServerWorld.tick(ServerWorld.java:316)

-- Affected level --
Details:
	All players: 1 total; [ServerPlayerEntity['Dev'/236, l='New World', x=-102.31, y=79.00, z=-212.43]]
	Chunk stats: ServerChunkCache: 2255
	Level dimension: DimensionType{minecraft:overworld}
	Level name: New World
	Level seed: -743399848020670749
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: {}
	Level spawn location: World: (-96,72,-224), Chunk: (at 0,4,0 in -6,-14; contains blocks -96,0,-224 to -81,255,-209), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
	Level time: 1446 game time, 1446 day time
	Known server brands: forge
	Level was modded: true
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 142250 (now: false), thunder time: 160957 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:849)
	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:784)
	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:114)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:637)
	at java.lang.Thread.run(Thread.java:748)

-- System Details --
Details:
	Minecraft Version: 1.15.2
	Minecraft Version ID: 1.15.2
	Operating System: Windows 10 (amd64) version 10.0
	Java Version: 1.8.0_191, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 1074515400 bytes (1024 MB) / 2050490368 bytes (1955 MB) up to 3801088000 bytes (3625 MB)
	CPUs: 12
	JVM Flags: 1 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump
	ModLauncher: 5.1.0+69+master.79f13f7
	ModLauncher launch target: fmluserdevclient
	ModLauncher naming: mcp
	ModLauncher services: 
		/eventbus-2.2.0-service.jar eventbus PLUGINSERVICE 
		/forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-launcher.jar object_holder_definalize PLUGINSERVICE 
		/forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-launcher.jar runtime_enum_extender PLUGINSERVICE 
		/accesstransformers-2.1.1-shadowed.jar accesstransformer PLUGINSERVICE 
		/forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-launcher.jar capability_inject_definalize PLUGINSERVICE 
		/forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-launcher.jar runtimedistcleaner PLUGINSERVICE 
		/forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-launcher.jar fml TRANSFORMATIONSERVICE 
	FML: 31.2
	Forge: net.minecraftforge:31.2.0
	FML Language Providers: 
		javafml@31.2
		minecraft@1
	Mod List: 
		client-extra.jar Minecraft {minecraft@1.15.2 DONE}
		main Onion Mod {onion@1.15.2_1.0.0 DONE}
		forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1.jar Forge {forge@31.2.0 DONE}
	Player Count: 1 / 8; [ServerPlayerEntity['Dev'/236, l='New World', x=-102.31, y=79.00, z=-212.43]]
	Data Packs: vanilla, mod:onion, mod:forge (incompatible)
	Type: Integrated Server (map_client.txt)
	Is Modded: Definitely; Client brand changed to 'forge'
[20:37:06] [Render thread/INFO] [STDOUT/]: [net.minecraft.util.registry.Bootstrap:printToSYSOUT:103]: #@!@# Game crashed! Crash report saved to: #@!@# .\crash-reports\crash-2020-06-03_20.37.06-server.txt
[20:37:06] [Server thread/INFO] [minecraft/ServerPlayNetHandler]: Dev lost connection: Disconnected
[20:37:06] [Server thread/INFO] [minecraft/MinecraftServer]: Dev left the game
AL lib: (EE) alc_cleanup: 1 device not closed

 

 

 

 

[Draco18s]

I haven't messed with entity predicates before, unfortunately, but it looks like something in EntityHasProperty.test() is throwing a null pointer.

[DeJunky]

Thanks for the response! Looks like I'm going to need to do some more reading and tinkering. I'll follow up if I run into any more trouble.

[Draco18s]

Creating new loot conditions isn't that hard. Vanilla has tons of examples, and while I haven't done a condition, I have done advancement triggers, which are pretty similar. If you don't know how to implement the interface directly, copy an existing implementation, find the test() method, modify to return true when you want it to be true (adding undefined variables for the conditions specified by the json file) and working backwards until the errors are gone.