feat: generate JSDoc from column comments

.github/workflows/ci.yml

@@ -15,10 +15,10 @@ jobs:
       TZ: "Europe/Paris"
       DO_NOT_TRACK: "1"
     steps:
-      - uses: "actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10" # v6.0.3
+      - uses: "actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1" # v7.0.1
 
       - name: "Setup Node.js"
-        uses: "actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e" # v6.4.0
+        uses: "actions/setup-node@820762786026740c76f36085b0efc47a31fe5020" # v7.0.0
         with:
           node-version: "24.16.0"
           cache: "npm"

.github/workflows/release.yml

@@ -17,13 +17,13 @@ jobs:
       pull-requests: "write"
       id-token: "write"
     steps:
-      - uses: "actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10" # v6.0.3
+      - uses: "actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1" # v7.0.1
         with:
           fetch-depth: 0
           persist-credentials: false
 
       - name: "Setup Node.js"
-        uses: "actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e" # v6.4.0
+        uses: "actions/setup-node@820762786026740c76f36085b0efc47a31fe5020" # v7.0.0
         with:
           node-version: "24.16.0"
           registry-url: "https://registry.npmjs.org"

README.md

@@ -168,6 +168,19 @@ const rows = await database.selectFrom("User").selectAll().execute()
 
 Fully type-safe queries derived from your actual database schema.
 
+### Column comments
+
+Column comments (`COMMENT ON COLUMN` in PostgreSQL, `COMMENT '...'` in MySQL) are emitted as JSDoc above the column, so they show up in your editor on hover:
+
+```ts
+export interface Users {
+  /** Contact email address. */
+  email: string | null
+}
+```
+
+SQLite has no column comments, so none are generated.
+
 ## Extending to other database dialects
 
 `kysely-typegen` ships with `KyselyTypegenPostgresDialect`, `KyselyTypegenMySQLDialect`, and `KyselyTypegenSQLiteDialect`, but you can add support for any database by extending the abstract `KyselyTypegenDialect` class.

package.json

@@ -41,23 +41,23 @@
     "release": "semantic-release"
   },
   "devDependencies": {
-    "@testcontainers/mysql": "12.0.1",
-    "@testcontainers/postgresql": "12.0.1",
-    "@types/better-sqlite3": "7.6.13",
-    "@types/node": "25.9.2",
-    "@types/pg": "8.20.0",
-    "better-sqlite3": "12.10.0",
-    "kysely": "0.29.2",
-    "kysely-postgres-js": "3.0.0",
-    "mysql2": "3.22.5",
-    "oxfmt": "0.54.0",
-    "oxlint": "1.69.0",
-    "oxlint-tsgolint": "0.23.0",
-    "pg": "8.21.0",
+    "@testcontainers/mysql": "12.2.0",
+    "@testcontainers/postgresql": "12.2.0",
+    "@types/better-sqlite3": "9.6.0",
+    "@types/node": "26.6.4",
+    "@types/pg": "8.23.1",
+    "better-sqlite3": "13.0.3",
+    "kysely": "0.29.6",
+    "kysely-postgres-js": "5.0.1",
+    "mysql2": "3.24.5",
+    "oxfmt": "0.71.0",
+    "oxlint": "1.86.0",
+    "oxlint-tsgolint": "7.0.2003",
+    "pg": "8.23.1",
     "postgres": "3.4.9",
-    "semantic-release": "25.0.3",
-    "tsdown": "0.22.2",
-    "typescript": "6.0.3"
+    "semantic-release": "25.0.9",
+    "tsdown": "0.23.0",
+    "typescript": "7.0.2"
   },
   "peerDependencies": {
     "kysely": ">=0.29.0"

src/_test/__snapshots__/mysql.test.ts.snapshot

@@ -62,10 +62,16 @@ exports[`typegen MySQL > generate types matching snapshot 1`] = `
     "}",
     "",
     "export interface Orders {",
+    "  /**",
+    "   * Total amount in cents.",
+    "   *",
+    "   * Excludes taxes.",
+    "   */",
     "  amountCents: number",
     "  createdAt: Generated<Timestamp>",
     "  currency: Generated<\\"EUR\\" | \\"GBP\\" | \\"USD\\">",
     "  id: Generated<Int8>",
+    "  /** Free text, may contain *\\\\/ characters. */",
     "  note: string | null",
     "  status: Generated<\\"cancelled\\" | \\"paid\\" | \\"pending\\" | \\"shipped\\">",
     "  userId: number",
@@ -73,6 +79,7 @@ exports[`typegen MySQL > generate types matching snapshot 1`] = `
     "",
     "export interface Users {",
     "  createdAt: Generated<Timestamp>",
+    "  /** Contact email address. */",
     "  email: string | null",
     "  id: Generated<number>",
     "  isActive: Generated<number>",

src/_test/__snapshots__/postgres.test.ts.snapshot

@@ -79,10 +79,16 @@ exports[`typegen PostgreSQL > generate types matching snapshot (kysely-postgres-
     "}",
     "",
     "export interface Orders {",
+    "  /**",
+    "   * Total amount in cents.",
+    "   *",
+    "   * Excludes taxes.",
+    "   */",
     "  amountCents: number",
     "  createdAt: Generated<Timestamp>",
     "  currency: Generated<Currency>",
     "  id: Generated<Int8>",
+    "  /** Free text, may contain *\\\\/ characters. */",
     "  note: string | null",
     "  status: Generated<OrderStatus>",
     "  userId: string",
@@ -90,6 +96,7 @@ exports[`typegen PostgreSQL > generate types matching snapshot (kysely-postgres-
     "",
     "export interface Users {",
     "  createdAt: Generated<Timestamp>",
+    "  /** Contact email address. */",
     "  email: string | null",
     "  id: Generated<string>",
     "  isActive: Generated<boolean>",
@@ -190,10 +197,16 @@ exports[`typegen PostgreSQL > generate types matching snapshot (pg) 1`] = `
     "}",
     "",
     "export interface Orders {",
+    "  /**",
+    "   * Total amount in cents.",
+    "   *",
+    "   * Excludes taxes.",
+    "   */",
     "  amountCents: number",
     "  createdAt: Generated<Timestamp>",
     "  currency: Generated<Currency>",
     "  id: Generated<Int8>",
+    "  /** Free text, may contain *\\\\/ characters. */",
     "  note: string | null",
     "  status: Generated<OrderStatus>",
     "  userId: string",
@@ -201,6 +214,7 @@ exports[`typegen PostgreSQL > generate types matching snapshot (pg) 1`] = `
     "",
     "export interface Users {",
     "  createdAt: Generated<Timestamp>",
+    "  /** Contact email address. */",
     "  email: string | null",
     "  id: Generated<string>",
     "  isActive: Generated<boolean>",

src/_test/mysql.test.ts

@@ -117,7 +117,9 @@ const createSchema = async (database: Kysely<any>): Promise<void> => {
     .addColumn("username", "varchar(50)", (column) => {
       return column.notNull().unique()
     })
-    .addColumn("email", "text")
+    .addColumn("email", "text", (column) => {
+      return column.modifyEnd(sql`comment ${sql.lit("Contact email address.")}`)
+    })
     .addColumn("role", sql`enum('admin','member','guest')`, (column) => {
       return column.notNull().defaultTo("member")
     })
@@ -144,9 +146,13 @@ const createSchema = async (database: Kysely<any>): Promise<void> => {
       return column.notNull().defaultTo("EUR")
     })
     .addColumn("amountCents", "integer", (column) => {
-      return column.notNull()
+      return column
+        .notNull()
+        .modifyEnd(sql`comment ${sql.lit("Total amount in cents.\n\nExcludes taxes.")}`)
+    })
+    .addColumn("note", "text", (column) => {
+      return column.modifyEnd(sql`comment ${sql.lit("Free text, may contain */ characters.")}`)
     })
-    .addColumn("note", "text")
     .addColumn("createdAt", "timestamp", (column) => {
       return column.notNull().defaultTo(sql`current_timestamp`)
     })

src/_test/postgres.test.ts

@@ -195,6 +195,16 @@ const createSchema = async (database: Kysely<any>): Promise<void> => {
       return column.notNull().defaultTo(sql`now()`)
     })
     .execute()
+
+  await sql`comment on column ${sql.ref("Users.email")} is ${sql.lit("Contact email address.")}`.execute(
+    database,
+  )
+  await sql`comment on column ${sql.ref("Orders.amountCents")} is ${sql.lit("Total amount in cents.\n\nExcludes taxes.")}`.execute(
+    database,
+  )
+  await sql`comment on column ${sql.ref("Orders.note")} is ${sql.lit("Free text, may contain */ characters.")}`.execute(
+    database,
+  )
 }
 
 describe("typegen PostgreSQL", () => {

src/index.ts

@@ -73,6 +73,24 @@ export abstract class KyselyTypegenDialect {
     return scalars[dataType] ?? "unknown"
   }
 
+  protected formatColumnComment(comment: string): string[] {
+    const trimmedComment = comment.trim()
+    if (trimmedComment.length === 0) {
+      return []
+    }
+    const lines = trimmedComment.replaceAll("*/", "*\\/").split(/\r?\n/u)
+    if (lines.length === 1) {
+      return [`  /** ${lines[0]} */`]
+    }
+    return [
+      "  /**",
+      ...lines.map((line) => {
+        return line.length === 0 ? "   *" : `   * ${line}`
+      }),
+      "   */",
+    ]
+  }
+
   public getTablesTypegen(
     tables: TableMetadata[],
     enums: EnumMetadata[],
@@ -94,6 +112,9 @@ export abstract class KyselyTypegenDialect {
         if (column.hasDefaultValue || column.isAutoIncrementing) {
           columnType = `Generated<${columnType}>`
         }
+        if (column.comment != null) {
+          result.push(...this.formatColumnComment(column.comment))
+        }
         result.push(`  ${column.name}: ${columnType}`)
       }
       result.push("}", "")
@@ -146,14 +167,16 @@ export abstract class KyselyTypegenDialect {
     tables: TableMetadata[]
   }> {
     const [tables, { enums, inlineEnums }] = await Promise.all([this.getTables(), this.getEnums()])
-    const lines: string[] = [...PREAMBLE_LINES]
-    lines.push(...this.getEnumsTypegen(enums))
-    lines.push(...this.getTablesTypegen(tables, enums, inlineEnums))
-    lines.push("export interface DB {")
-    for (const table of tables) {
-      lines.push(`  ${table.name}: ${table.name}`)
-    }
-    lines.push("}")
+    const lines: string[] = [
+      ...PREAMBLE_LINES,
+      ...this.getEnumsTypegen(enums),
+      ...this.getTablesTypegen(tables, enums, inlineEnums),
+      "export interface DB {",
+      ...tables.map((table) => {
+        return `  ${table.name}: ${table.name}`
+      }),
+      "}",
+    ]
     return { lines, enums, inlineEnums, tables }
   }
 }

src/mysql.ts

@@ -52,12 +52,12 @@ export class KyselyTypegenMySQLDialect extends KyselyTypegenDialect {
       ])
       .where("columns.TABLE_SCHEMA", "=", sql`database()`)
       .where("columns.DATA_TYPE", "in", ["enum", "set"])
+      .$castTo<{ tableName: string; columnName: string; columnType: string }>()
       .execute()
 
     const inline = new Map<string, string[]>()
     for (const row of rows) {
-      const data = row as { tableName: string; columnName: string; columnType: string }
-      inline.set(`${data.tableName}.${data.columnName}`, parseMysqlEnumColumnType(data.columnType))
+      inline.set(`${row.tableName}.${row.columnName}`, parseMysqlEnumColumnType(row.columnType))
     }
     return { named: [], inline }
   }