[Documentation] Document kone-db

documentation/databases.md

@@ -4,6 +4,86 @@ Oodikone uses three separate databases, each for different purposes. This docume
 
 Please note that each database may contain additional information such as migration tables or indices that are not depicted here. For more details, inspect the actual databases via the commandline.
 
+In the tables, `PK` marks primary key(s), `FK` marks foreign keys and `UK` mark unique keys. Refer to the official [Mermaid.js documentation](https://mermaid.js.org/syntax/entityRelationshipDiagram.html) for full syntax.
+
+## kone-db
+
+The `kone-db` database contains information used in various features of Oodikone. This functionality is native to Oodikone and not necessarily directly related to Sisu.
+
+```mermaid
+erDiagram
+  custom_population_searches {
+    bigint         id       PK "not null"
+    bigint         userId
+    varchar(255)   name        "not null"
+    varchar(255)[] students
+    timestamp      createdAt
+    timestamp      updatedAt
+  }
+  excluded_courses {
+    integer      id                 PK "not null"
+    varchar(255) programme_code
+    varchar(255) course_code
+    timestamp    created_at
+    timestamp    updated_at
+    varchar(255) curriculum_version
+  }
+  open_uni_population_searches {
+    bigint         id           PK "not null"
+    bigint         user_id
+    varchar(255)   name            "not null"
+    varchar(255)[] course_codes
+    timestamp      created_at
+    timestamp      updated_at
+  }
+  progress_criteria {
+    varchar(255)   code               PK "not null"
+    varchar(255)[] courses_year_one
+    varchar(255)[] courses_year_two
+    varchar(255)[] courses_year_three
+    integer        credits_year_one
+    integer        credits_year_two
+    integer        credits_year_three
+    timestamp      created_at
+    timestamp      updated_at
+    varchar(255)[] courses_year_four
+    varchar(255)[] courses_year_five
+    varchar(255)[] courses_year_six
+    integer        credits_year_four
+    integer        credits_year_five
+    integer        credits_year_six
+    varchar(255)   curriculum_version
+  }
+  study_guidance_group_tags {
+    bigint       id                      PK "no null"
+    varchar(255) study_guidance_group_id UK
+    varchar(255) study_programme
+    varchar(255) year
+    timestamp    created_at
+    timestamp    updated_at
+  }
+  study_programme_pins {
+    integer        user_id          PK "not null"
+    varchar(255)[] study_programmes
+  }
+  tag ||--o{ tag_student : "belongs to"
+  tag {
+    timestamp    createdAt
+    timestamp    updatedAt
+    varchar(255) tagname
+    varchar(255) studytrack          "not null"
+    bigint       tag_id           PK "not null"
+    varchar(255) year
+    bigint       personal_user_id
+  }
+  tag_student {
+    timestamp    createdAt
+    timestamp    updatedAt
+    varchar(255) studentnumber PK     "not null"
+    bigint       tag_id        PK, FK "not null"
+  }
+```
+
 ## user-db
 
 The `user-db` database contains information about users of Oodikone.