Kura

Database layer for Erlang - Ecto-equivalent abstractions in pure Erlang. Pluggable backends: kura_postgres (PostgreSQL via pgo), kura_sqlite (SQLite via esqlite).

Features

• Schema - behaviour-based schema definitions with type metadata
• Changeset - cast external params, validate, track changes and errors
• Query Builder - composable, functional query construction
• SQL Compiler - parameterized SQL generation (no string interpolation)
• Repo - CRUD operations with automatic type conversion and PG error mapping
• Associations - belongs_to, has_one, has_many, many_to_many with preloading
• Embedded Schemas - embeds_one, embeds_many stored as JSONB
• Multi - atomic transaction pipelines
• Migrations - DDL operations with automatic module-based discovery
• Enums - atom-backed enum types stored as VARCHAR
• Telemetry - query logging with timing
• Lifecycle Hooks - before/after callbacks for insert, update, delete
• Audit Trail - automatic change tracking with actor context
• Pagination - offset-based and cursor-based pagination
• Streaming - server-side cursor streaming for large result sets
• Multitenancy - schema prefix and attribute-based tenant isolation
• Optimistic Locking - concurrent update conflict detection

Quick Start

Define a Schema

-module(user).
-behaviour(kura_schema).
-include_lib("kura/include/kura.hrl").

-export([table/0, fields/0]).

table() -> ~"users".

fields() ->
    [
        #kura_field{name = id, type = id, primary_key = true, nullable = false},
        #kura_field{name = name, type = string, nullable = false},
        #kura_field{name = email, type = string, nullable = false},
        #kura_field{name = age, type = integer},
        #kura_field{name = inserted_at, type = utc_datetime},
        #kura_field{name = updated_at, type = utc_datetime}
    ].

Define a Repo

-module(my_repo).
-behaviour(kura_repo).

-export([otp_app/0, start/0, all/1, get/2, insert/1, update/1, delete/1]).

otp_app() -> my_app.

start() -> kura_repo_worker:start(?MODULE).
all(Q) -> kura_repo_worker:all(?MODULE, Q).
get(Schema, Id) -> kura_repo_worker:get(?MODULE, Schema, Id).
insert(CS) -> kura_repo_worker:insert(?MODULE, CS).
update(CS) -> kura_repo_worker:update(?MODULE, CS).
delete(CS) -> kura_repo_worker:delete(?MODULE, CS).

Configure the database connection in sys.config:

[{my_app, [
    {my_repo, #{
        database => ~"myapp",
        hostname => ~"localhost",
        port => 5432,
        username => ~"postgres",
        password => <<>>,
        pool_size => 10
    }}
]}].

Changesets

%% Cast and validate external params
CS = kura_changeset:cast(user, #{}, #{~"name" => ~"Alice", ~"email" => ~"alice@example.com"}, [name, email, age]),
CS1 = kura_changeset:validate_required(CS, [name, email]),
CS2 = kura_changeset:validate_format(CS1, email, ~"@"),
CS3 = kura_changeset:validate_length(CS2, name, [{min, 1}, {max, 100}]),

%% Insert
{ok, User} = my_repo:insert(CS3).

Query Builder

Q = kura_query:from(user),
Q1 = kura_query:where(Q, {age, '>', 18}),
Q2 = kura_query:where(Q1, {'or', [{role, ~"admin"}, {role, ~"moderator"}]}),
Q3 = kura_query:select(Q2, [name, email]),
Q4 = kura_query:order_by(Q3, [{name, asc}]),
Q5 = kura_query:limit(Q4, 10),

{ok, Users} = my_repo:all(Q5).

Supported conditions: =, !=, <, >, <=, >=, like, ilike, in, not_in, is_nil, is_not_nil, between, {'and', [...]}, {'or', [...]}, {'not', ...}, {fragment, SQL, Params}.

Migrations

-module(m20240115120000_create_users).
-behaviour(kura_migration).
-include_lib("kura/include/kura.hrl").

-export([up/0, down/0]).

up() ->
    [{create_table, ~"users", [
        #kura_column{name = id, type = id, primary_key = true, nullable = false},
        #kura_column{name = name, type = string, nullable = false},
        #kura_column{name = email, type = string, nullable = false},
        #kura_column{name = age, type = integer},
        #kura_column{name = inserted_at, type = utc_datetime},
        #kura_column{name = updated_at, type = utc_datetime}
    ]},
    {create_index, ~"users", [email], #{unique => true}}].

down() ->
    [{drop_index, ~"users_email_index"},
     {drop_table, ~"users"}].

Run migrations:

kura_migrator:migrate(my_repo).
kura_migrator:rollback(my_repo).
kura_migrator:status(my_repo).

Type Mapping

SQLite values round-trip transparently via kura_types:cast/2 (booleans 0/1 → true/false, ISO 8601 → datetime tuples, JSON text → maps).

Configuration

Configure repos under the kura app env. Each repo is a map keyed by its module name; pick a backend package and Kura starts the configured pool at app boot, populating dialect, pool_module, and driver_module from the aggregator automatically.

%% sys.config — single Postgres repo
[{kura, [
    {repos, #{
        my_repo => #{
            backend => kura_backend_postgres,
            host => "localhost",
            port => 5432,
            database => "my_app_dev",
            user => "postgres",
            password => "postgres",
            pool_size => 10
        }
    }}
]}].

%% sys.config — single SQLite repo
[{kura, [
    {repos, #{
        my_repo => #{
            backend => kura_backend_sqlite,
            database => <<"my_app.db">>,   %% or <<":memory:">>
            pool_size => 4
        }
    }}
]}].

%% sys.config — Postgres primary + SQLite analytics
[{kura, [
    {repos, #{
        my_repo => #{
            backend => kura_backend_postgres,
            host => "localhost",
            database => "main",
            user => "postgres",
            pool_size => 10
        },
        analytics_repo => #{
            backend => kura_backend_sqlite,
            database => <<":memory:">>
        }
    }}
]}].

Each repo module declares itself in code:

-module(my_repo).
-behaviour(kura_repo).
-export([otp_app/0]).
otp_app() -> my_app.

Queries through my_repo emit Postgres SQL; queries through analytics_repo emit SQLite SQL. The query cache is keyed per repo so the dialects never share entries. UUID primary keys are auto-generated on insert when no value is provided.

[{kura, [
    {repo, my_repo},
    {backend, kura_backend_postgres},
    {host, "localhost"},
    {port, 5432},
    {database, "my_app_dev"},
    {user, "postgres"},
    {password, "postgres"},
    {pool_size, 10}
]}].

[{my_app, [
    {my_repo, #{
        backend => kura_backend_postgres,
        database => ~"my_app_dev",
        hostname => ~"localhost",
        port => 5432,
        username => ~"postgres",
        password => ~"postgres",
        pool_size => 10
    }}
]}].

Migrations are discovered automatically from compiled modules implementing the kura_migration behaviour.

Optional telemetry/logging config:

[{kura, [
    {log, true}  %% true | {M, F} | false (default)
]}].

Plugins

• rebar3_kura - Rebar3 plugin that auto-generates migration files from schema changes. Add a field to your schema, run rebar3 compile, and the migration is created for you.
• opentelemetry_kura - OpenTelemetry instrumentation. Subscribes to Kura's telemetry events and creates spans for every database query.

Examples

• pet_store - A sample REST API built with Kura and Nova demonstrating schemas, changesets, queries, migrations, and associations in practice.

Requirements

• Erlang/OTP 28+
• One backend: PostgreSQL 14+ (via kura_postgres) or SQLite 3.35+ (via kura_sqlite)