Comment introspection implementation for mssql, mysql and postgres

Signed-off-by: Makara Sok <me@maktouch.com>

src/dialect/database-introspector.ts

@@ -68,4 +68,5 @@ export interface ColumnMetadata {
   readonly isAutoIncrementing: boolean
   readonly isNullable: boolean
   readonly hasDefaultValue: boolean
+  readonly comment?: string
 }

src/dialect/mssql/mssql-introspector.ts

@@ -48,6 +48,13 @@ export class MssqlIntrospector implements DatabaseIntrospector {
         'type_schemas.schema_id',
         'types.schema_id'
       )
+      .leftJoin(
+        'sys.extended_properties as comments',
+        join => join
+          .onRef('comments.major_id', '=', 'tables.object_id')
+          .onRef('comments.minor_id', '=', 'columns.column_id')
+          .on('comments.name', '=', 'MS_Description')
+      )
       .$if(!options.withInternalKyselyTables, (qb) =>
         qb
           .where('tables.name', '!=', DEFAULT_MIGRATION_TABLE)
@@ -74,6 +81,7 @@ export class MssqlIntrospector implements DatabaseIntrospector {
         'types.is_nullable as type_is_nullable',
         'types.name as type_name',
         'type_schemas.name as type_schema_name',
+        'comments.value as column_comment'
       ])
       .unionAll(
         this.#db
@@ -98,6 +106,13 @@ export class MssqlIntrospector implements DatabaseIntrospector {
             'type_schemas.schema_id',
             'types.schema_id'
           )
+          .leftJoin(
+            'sys.extended_properties as comments',
+            join => join
+              .onRef('comments.major_id', '=', 'views.object_id')
+              .onRef('comments.minor_id', '=', 'columns.column_id')
+              .on('comments.name', '=', 'MS_Description')
+          )
           .select([
             'views.name as table_name',
             'views.type as table_type',
@@ -112,6 +127,7 @@ export class MssqlIntrospector implements DatabaseIntrospector {
             'types.is_nullable as type_is_nullable',
             'types.name as type_name',
             'type_schemas.name as type_schema_name',
+            'comments.value as column_comment'
           ])
       )
       .orderBy('table_schema_name')
@@ -147,6 +163,7 @@ export class MssqlIntrospector implements DatabaseIntrospector {
           isNullable:
             rawColumn.column_is_nullable && rawColumn.type_is_nullable,
           name: rawColumn.column_name,
+          comment: rawColumn.column_comment ?? undefined,
         })
       )
     }
@@ -204,6 +221,12 @@ interface MssqlSysTables {
     // scale: number
     system_type_id: number
   }
+  'sys.extended_properties': {
+    major_id: number
+    minor_id: number
+    name: string
+    value: string
+  }
   'sys.schemas': {
     name: string
     // principal_id: number

src/dialect/mysql/mysql-introspector.ts

@@ -50,6 +50,7 @@ export class MysqlIntrospector implements DatabaseIntrospector {
         'columns.IS_NULLABLE',
         'columns.DATA_TYPE',
         'columns.EXTRA',
+        'columns.COLUMN_COMMENT',
       ])
       .where('columns.TABLE_SCHEMA', '=', sql`database()`)
       .orderBy('columns.TABLE_NAME')
@@ -96,6 +97,7 @@ export class MysqlIntrospector implements DatabaseIntrospector {
           isNullable: it.IS_NULLABLE === 'YES',
           isAutoIncrementing: it.EXTRA.toLowerCase().includes('auto_increment'),
           hasDefaultValue: it.COLUMN_DEFAULT !== null,
+          comment: it.COLUMN_COMMENT === '' ? undefined : it.COLUMN_COMMENT
         })
       )
 
@@ -117,4 +119,5 @@ interface RawColumnMetadata {
   IS_NULLABLE: 'YES' | 'NO'
   DATA_TYPE: string
   EXTRA: string
+  COLUMN_COMMENT: string
 }

src/dialect/postgres/postgres-introspector.ts

@@ -57,7 +57,7 @@ export class PostgresIntrospector implements DatabaseIntrospector {
         'ns.nspname as schema',
         'typ.typname as type',
         'dtns.nspname as type_schema',
-
+        sql<string | null>`col_description(a.attrelid, a.attnum)`.as('column_description'),
         // Detect if the column is auto incrementing by finding the sequence
         // that is created for `serial` and `bigserial` columns.
         this.#db
@@ -126,6 +126,7 @@ export class PostgresIntrospector implements DatabaseIntrospector {
           isNullable: !it.not_null,
           isAutoIncrementing: !!it.auto_incrementing,
           hasDefaultValue: it.has_default,
+          comment: it.column_description ?? undefined
         })
       )
 
@@ -148,4 +149,5 @@ interface RawColumnMetadata {
   type: string
   type_schema: string
   auto_incrementing: boolean | null
+  column_description: string | null
 }

src/dialect/sqlite/sqlite-introspector.ts

@@ -94,6 +94,7 @@ export class SqliteIntrospector implements DatabaseIntrospector {
         isNullable: !col.notnull,
         isAutoIncrementing: col.name === autoIncrementCol,
         hasDefaultValue: col.dflt_value != null,
+        comment: undefined
       })),
     }
   }