Add get_party_description function and Liquibase migration

.gitignore

@@ -1,4 +1,6 @@
 out/
+liquibase/liquibase.local.properties
+liquibase/lib/
 devel/pg/src
 devel/pg/1*
 devel/pg/data*

cli/scripts/sql/get_party_description.sql

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+-- Read-only PL/pgSQL helper for party.description.
+--
+-- Expected table (adjust names/types to match your schema):
+--   CREATE TABLE party (
+--     party_id    bigint PRIMARY KEY,
+--     description text
+--   );
+
+CREATE OR REPLACE FUNCTION get_party_description(p_party_id bigint)
+RETURNS text
+LANGUAGE plpgsql
+STABLE
+STRICT
+PARALLEL SAFE
+SECURITY INVOKER
+SET search_path = ''
+AS $function$
+DECLARE
+    v_description text;
+BEGIN
+    SELECT p.description
+      INTO v_description
+      FROM public.party AS p
+     WHERE p.party_id = p_party_id;
+
+    RETURN v_description;
+END;
+$function$;
+
+COMMENT ON FUNCTION get_party_description(bigint) IS
+    'Returns description for the given party_id; NULL if the row does not exist.';

liquibase/README.md

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+# Liquibase
+
+Database migrations for PostgreSQL. **SQL files are plain PostgreSQL** — no Liquibase directives inside them. Liquibase metadata lives only in the small XML changelogs that reference those files via `sqlFile`.
+
+## Layout
+
+```
+liquibase/
+  liquibase.properties
+  changelog/
+    db.changelog-master.xml
+    changes/
+      001-get-party-description.xml          # changeset (sqlFile refs only)
+      001-get-party-description.sql          # native SQL
+      001-get-party-description-rollback.sql # native rollback SQL
+```
+
+## Prerequisites
+
+- [Liquibase CLI](https://docs.liquibase.com/start/install/home.html)
+- PostgreSQL JDBC driver on the classpath (or Liquibase 4.29+ with bundled drivers)
+
+## Configure
+
+```bash
+cp liquibase.properties.example liquibase.local.properties
+# edit liquibase.local.properties with your JDBC URL and credentials
+```
+
+`liquibase.local.properties` is gitignored.
+
+## Run
+
+```bash
+cd liquibase
+liquibase update
+```
+
+Preview SQL:
+
+```bash
+liquibase update-sql
+```
+
+Rollback:
+
+```bash
+liquibase rollback-count 1
+```
+
+You can also run the native `.sql` files directly with `psql` if you are not using Liquibase.
+
+## Changesets
+
+| Id | Apply SQL | Rollback SQL |
+|----|-----------|--------------|
+| `001-get-party-description` | `changes/001-get-party-description.sql` | `changes/001-get-party-description-rollback.sql` |
+
+`splitStatements="false"` is set on `sqlFile` so PostgreSQL `$function$` delimiters are not split.

liquibase/changelog/changes/001-get-party-description-rollback.sql

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+DROP FUNCTION IF EXISTS public.get_party_description(bigint);

liquibase/changelog/changes/001-get-party-description.sql

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+CREATE OR REPLACE FUNCTION public.get_party_description(p_party_id bigint)
+RETURNS text
+LANGUAGE plpgsql
+STABLE
+STRICT
+PARALLEL SAFE
+SECURITY INVOKER
+SET search_path = ''
+AS $function$
+DECLARE
+    v_description text;
+BEGIN
+    SELECT p.description
+      INTO v_description
+      FROM public.party AS p
+     WHERE p.party_id = p_party_id;
+
+    RETURN v_description;
+END;
+$function$;
+
+COMMENT ON FUNCTION public.get_party_description(bigint) IS
+    'Returns description for the given party_id; NULL if the row does not exist.';

liquibase/changelog/changes/001-get-party-description.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<databaseChangeLog
+    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
+        https://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
+
+    <changeSet id="001-get-party-description" author="ctl">
+        <comment>Read-only PL/pgSQL function get_party_description(party_id)</comment>
+
+        <sqlFile
+            path="001-get-party-description.sql"
+            relativeToChangelogFile="true"
+            splitStatements="false"/>
+
+        <rollback>
+            <sqlFile
+                path="001-get-party-description-rollback.sql"
+                relativeToChangelogFile="true"
+                splitStatements="false"/>
+        </rollback>
+    </changeSet>
+
+</databaseChangeLog>

liquibase/changelog/db.changelog-master.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<databaseChangeLog
+    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
+        https://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
+
+    <include file="changes/001-get-party-description.xml" relativeToChangelogFile="true"/>
+
+</databaseChangeLog>

liquibase/liquibase.properties

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+# Copy to liquibase.local.properties and override for your environment.
+# Liquibase loads liquibase.local.properties automatically when present.
+
+changeLogFile=changelog/db.changelog-master.xml
+
+url=jdbc:postgresql://localhost:5432/ctl
+username=postgres
+password=
+
+driver=org.postgresql.Driver
+classpath=lib/postgresql.jar
+
+logLevel=info

liquibase/liquibase.properties.example

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+changeLogFile=changelog/db.changelog-master.xml
+
+url=jdbc:postgresql://localhost:5432/your_database
+username=your_user
+password=your_password
+
+driver=org.postgresql.Driver