When you create a Block with BlockEntity, you might want to place the block with predefined Nbt data from an ItemStack (of your BlockItem), or save the BlockEntity data in the ItemStack after breaking the block.

Before proceeding, you will need a Block (with BlockItem) and a BlockEntity.

For a block to drop an ItemStack with the Nbt from the BlockEntity of the broken block, we only need to change the loot table:

src/main/resources/data/tutorial/loot_tables/blocks/demo_block.json

{
  "type": "minecraft:block",
  "pools": [
    {
      "rolls": 1.0,
      "entries": [
        {
          "type": "minecraft:item",
          "name": "tutorial:demo_block",
          "functions": [
            {
              "function": "minecraft:copy_nbt",
              "source": "block_entity",
              "ops": [
                {
                  "source": "number",
                  "target": "BlockEntityTag.number",
                  "op": "replace"
                }
              ]
            }
          ]
        }
      ]
    }
  ]
}

Where:

• source is the Tag key String we used in the writeNbt and readNbt methods in our DemoBlockEntity class – “number”
• target is the Tag key hierarchy in the dropped ItemStack (source prefixed with the “BlockEntityTag” key, which is needed for placing the block back with the saved data) – “BlockEntityTag.number”

To save more fields, just add more replace operations (with source, target and op) to the “ops” array.