Pathom

Pathom is an open-source data querying and resolution library for Clojure and ClojureScript. It provides a declarative parser that synthesizes data from a set of resolvers, enabling GraphQL-like queries against diverse data sources. Pathom is commonly used with Fulcro to define how a frontend retrieves structured data from a backend.

Core concepts in Pathom include resolvers, the parser, and the environment. A resolver is a small, reusable function that declares its input dependencies and the outputs it produces. In Pathom they are typically defined with a defresolver construct and describe the keys they read from the environment and the keys they return. The parser composes many resolvers into a plan that matches a requested query, resolving dependencies in the correct order. The environment (env) holds data sources such as databases, services, or caches, and may be augmented as resolvers run.

How it works: a client issues a query describing the desired data. Pathom analyzes which resolvers can provide the requested attributes, builds a plan, executes resolvers in dependency order (supporting asynchronous operations when needed), and returns a normalized map of results. It can handle nested and related data through resolver composition and “join” semantics.

Usage and ecosystem: Pathom is designed to work server-side with Clojure, often in concert with Fulcro to streamline data fetching for UI layers. It is adaptable to various backends and data sources via resolvers, offering a flexible alternative to traditional REST or GraphQL approaches.