Patches found inside the prepatches folder of a mod's assets will run before any regular patches are processed, guaranteeing the ability to patch standard patches before they have run.

Patches found inside the postpatches folder of a mod's assets will run after all prepatches and patches are processed.

Adds the ability to use Newtonsoft's JPath queries to define more expressive and dynamic patches. This feature is available for use in patches found in patches, prepatches, and postpatches.

To utilize JPath queries, place your query inside the path field of your patch.

If you expect and want your patch to apply to multiple elements in the target file, be sure to add "patchMultiple": true to your patch.

When performing an add or addeach patch operation using JPath queries, because the element being added does not exist yet and would cause the query to fail, it must be left out of the path definition. Instead, add the new element name (or index) to pathAppend. The string found in pathAppend will be added to the end of the pointers found by your JPath query before patching the target file. pathAppend does not support JPath and must be in vanilla's standard JsonPointer notation.

You'd like to mod the panning loot table so that temporal gears are far more common from both sand/gravel and bony soil. (Excerpt from pan.json as of Vintage Story v1.18.0)

{
  "code": "pan",
  "attributes": {
    "panningDrops": {
      "@(bonysoil|bonysoil-.*)": [
        // ... 17 other items not shown
        { "type": "item", "code": "gear-temporal",  "chance": { "avg": 0.001, "var": 0 }  },
        // ...
      ],
      "@(sand|gravel)-.*": [
        // ... 19 other items not shown
        { "type": "item", "code": "gear-temporal",  "chance": { "avg": 0.0005, "var": 0 }  },
        // ...
      ]
    }
  }
}

If you were to write a patch file for this in the vanilla patching system (or use modmaker.exe), your patch file would look like this:

[
  {
    "op": "replace",
    "path": "/attributes/panningDrops/@(bonysoil|bonysoil-.*)/17/chance/avg",
    "value": 20,
    "file": "game:blocktypes/wood/pan.json",
    "side": "Server"
  },
  {
    "op": "replace",
    "path": "/attributes/panningDrops/@(sand|gravel)-.*/19/chance/avg",
    "value": 20,
    "file": "game:blocktypes/wood/pan.json",
    "side": "Server"
  }
]

These patches are brittle to any changes to the drop tables in vanilla as well as from other mods due to the array indexes shifting from additions and deletions. Also, you and anyone reading your patch have no idea which item in the drop table is being changed without referencing pan.json.

Using a JPath query instead, your patch might look like this:

[
  {
    "op": "replace",
    "path": "$.attributes.panningDrops.*..[?(@..code == 'gear-temporal')].chance.avg",
    "value": 20,
    "patchMultiple": true,
    "file": "game:blocktypes/wood/pan.json",
    "side": "Server"
  }
]

Now the patch is expressive and resilient to vanilla and third party mod adjustments. The leading $ signifies the root element. A . followed by a key finds the appropriately named child element. .* selects all of the current element's children. In this example, this is both the @(bonysoil|bonysoil-.*) and @(sand|gravel)-.* elements, but also includes any potential additions and changes to panningDrops. A .. indicates any descendant element from the current point in the tree. [?()] is a JPath filter expression. @ inside the expression represents the current element. In this example, [?(@..code == 'gear-temporal')] finds any element which has any descendant element key named code with a value of gear-temporal. The remaining portion of the query, .chance.avg, continues traversing the tree to the element where the changes need to be made.

This patch file now has the flexibility to handle many potential changes from vanilla and third party mods.

As a final example, the below patch would raise the chance for cabbage seed drops to 1 for all crop stages where the current chance is less than 1.

[
  {
    "op": "replace",
    "path": "$.dropsByType.*..[?(@.code == 'seeds-cabbage' && @..avg < 1)]..avg",
    "value": 1,
    "patchMultiple": true,
    "file": "game:blocktypes/plant/crop/cabbage.json",
    "side": "Server"
  }
]

Log messages have been expanded to help with troubleshooting. Along with standard errors and summaries that appear in server-main and client-main, there are additional messages located in server-debug and client-debug to further explain both failed and successful patches.

[VerboseDebug] Patch 0 in patchwars:prepatches/jpathtest1.json: Found 2 paths using supplied JPath ($.attributes.panningDrops.*..[?(@..code == 'gear-temporal')].chance.avg): /attributes/panningDrops/@(bonysoil|bonysoil-.*)/17/chance/avg, /attributes/panningDrops/@(sand|gravel)-.*/19/chance/avg