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GraphQL API from an RDBMS Connection

Phrag implements its approach to creating GraphQL from an RDBMS connection for instant, flexible and customizable CRUD operations.

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Here is a live demo of Phrag's GraphQL connecting to a DB of this schema. You can try what Phrag creates just from a database provided.


  • Instantly Operational: Phrag creates a GraphQL simply from a RDBMS connection, retrieving schema data of tables, columns, primary keys and foreign keys. It can run as part of a Clojure project or stand-alone releases.

  • CRUD Features: tables and/or views become queryable as root objects including nested objects of n-ary relationships with aggregation, filter, sorting and pagination supported. Mutations (create, update and delete) are also created per table.

  • Customization: Phrag comes with an interceptor capability to customize behaviors of GraphQL. Custom functions can be configured per table & operation type and at pre/post DB operations. It can make a GraphQL service more practical with access controls, event firing and more.

  • Performance in Mind: Phrag's query resolver translates a nested object query into a single SQL query, leveraging correlated subqueries and JSON functions. Load tests have also been performed to verify it scales linear with resources without obvious bottlenecks.

  • Practicality in Mind: Phrag was developed side by side with a POC project to verify its concept and validate the practicality.


Phrag only requires an RDBMS to create its GraphQL API. Here's a quick view of database constructs that are important for Phrag. Detailed mechanism is explained here.

  • Primary keys: Phrag uses primary keys as identifiers of GraphQL mutations. Composite primary key is supported.

  • Foreign keys: Phrag translates foreign keys to nested properties in GraphQL query objects.

  • Indices on foreign key columns: Phrag queries a database by both origin and destination columns of foreign keys for nested objects. It should be noted that creating a foreign key does not always index those columns (especially origin column).


  • Supported databases are SQLite and PostgreSQL.

  • If PostgreSQL is used, Phrag queries usage tables such as key_column_usage and constraint_column_usage to retrieve PK / FK info, therefore a database user provided to Phrag needs to be identical to the one that created those keys.

  • Not all database column types are mapped to Phrag's GraphQL fields yet. Any help would be appreciated through issues and PRs.


Clojure Project

Phrag's GraphQL can be created with phrag.core/schema function and invoked through phrag.core/exec function:

(let [config {:db (hikari/make-datasource my-spec)}
      schema (phrag/schema config)]
  (phrag/exec config schema query vars req))

There is also a support for creating Phrag's GraphQL as a route for reitit or Bidi:

;; Add a route (path & handler) into a ring router:
(ring/router (phrag.route/reitit {:db my-datasource})

;; Also callable as an Integrant config map key
{:phrag.route/reitit {:db (ig/ref :my/datasource)}}


Database (:db) is the only required parameter in config, but there are many more configurable options. Please refer to configuration doc for details.

Stand-alone Releases

There is a stand-alone version of Phrag which is runnable as a Docker container or Java process with a single command. It's suitable if Phrag's GraphQL is desired without any custom logic or if one wants to play around with it. Here is the repository of those artifacts for more details.

Try it out as a Docker container with a self-contained DB:

docker run -it -p 3000:3000 ykskb/phrag-standalone:latest
# visit http://localhost:3000/graphiql/index.html

Run as a Docker container with your SQLite:

docker run -it -p 3000:3000 \
-v /host/db/dir:/database \ # mount a directory of your database
-e JDBC_URL=jdbc:sqlite:/database/db.sqlite \ # specify DB URL
# visit http://localhost:3000/graphiql/index.html


POC Project:

  • SNS: a situated project of Twitter mock to verify Phrag's concept and practicality. It has authentication, access control and custom logics through Phrag's interceptors, leveraging Phrag's GraphQL for queries with many nests and conditions.

Contribution to Phrag

Please feel free to open Github issues to send suggestions, report bugs or discuss features. PRs are also welcomed.

Copyright © 2021 Yohei Kusakabe

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