Hooks

Hooks are user-defined callbacks called either from the ctx.fire_hook method or by the job scheduler.

Let's assume we want to calculate some statistics on-demand to avoid blocking an indexer with heavy computations. Add the following lines to the DipDup config:

hooks:
  calculate_stats:
    callback: calculate_stats
    atomic: False
    args:
     major: bool
     depth: int

Here are a couple of things here to pay attention to:

  • An atomic option defines whether the hook callback will be wrapped in a single SQL transaction or not. If this option is set to true main indexing loop will be blocked until hook execution is complete. Some statements, like REFRESH MATERIALIZED VIEW, do not require to be wrapped in transactions, so choosing a value of the atomic option could decrease the time needed to perform initial indexing.
  • Values of args mapping are used as type hints in a signature of a generated callback. We will return to this topic later in this article.

Now it's time to call dipdup init. The following files will be created in the project's root:

├── hooks
│   └── calculate_stats.py
└── sql
    └── calculate_stats
        └── .keep

Content of the generated callback stub:

from dipdup.context import HookContext

async def calculate_stats(
    ctx: HookContext,
    major: bool,
    depth: int,
) -> None:
    await ctx.execute_sql('calculate_stats')

By default, hooks execute SQL scripts from the corresponding subdirectory of sql/. Remove or comment out the execute_sql call to prevent this. This way, both Python and SQL code may be executed in a single hook if needed.

Arguments typechecking

DipDup will ensure that arguments passed to the hooks have the correct types when possible. CallbackTypeError exception will be raised otherwise. Values of an args mapping in a hook config should be either built-in types or __qualname__ of external type like decimal.Decimal. Generic types are not supported: hints like Optional[int] = None will be correctly parsed during codegen but ignored on type checking.

💡 SEE ALSO