Action Michael's feedback about the structure of this feature.

packages/server/src/api/controllers/table/index.ts

@@ -11,7 +11,6 @@ import {
   BulkImportRequest,
   BulkImportResponse,
   FetchTablesResponse,
-  InternalTable,
   MigrateRequest,
   MigrateResponse,
   SaveTableRequest,
@@ -19,8 +18,6 @@ import {
   Table,
   TableResponse,
   UserCtx,
-  isBBReferenceField,
-  isRelationshipField,
 } from "@budibase/types"
 import sdk from "../../../sdk"
 import { jsonFromCsvString } from "../../../utilities/csv"
@@ -164,53 +161,8 @@ export async function validateExistingTableImport(ctx: UserCtx) {
   }
 }
 
-function error(ctx: UserCtx, message: string, status = 400) {
-  ctx.status = status
-  ctx.body = { message }
-}
-
 export async function migrate(ctx: UserCtx<MigrateRequest, MigrateResponse>) {
   const { tableId, oldColumn, newColumn } = ctx.request.body
-
-  // For now we're only supporting migrations of user relationships to user
-  // columns in internal tables. In future we may want to support other
-  // migrations but for now return an error if we aren't migrating a user
-  // relationship.
-  if (isExternalTable(tableId)) {
-    return error(ctx, "External tables cannot be migrated")
-  }
-
   const table = await sdk.tables.getTable(tableId)
-
-  if (!(oldColumn.name in table.schema)) {
-    return error(
-      ctx,
-      `Column "${oldColumn.name}" does not exist on table "${table.name}"`
-    )
-  }
-
-  if (newColumn.name in table.schema) {
-    return error(
-      ctx,
-      `Column "${newColumn.name}" already exists on table "${table.name}"`
-    )
-  }
-
-  if (!isBBReferenceField(newColumn)) {
-    return error(ctx, `Column "${newColumn.name}" is not a user column`)
-  }
-
-  if (newColumn.subtype !== "user" && newColumn.subtype !== "users") {
-    return error(ctx, `Column "${newColumn.name}" is not a user column`)
-  }
-
-  if (!isRelationshipField(oldColumn)) {
-    return error(ctx, `Column "${oldColumn.name}" is not a user relationship`)
-  }
-
-  if (oldColumn.tableId !== InternalTable.USER_METADATA) {
-    return error(ctx, `Column "${oldColumn.name}" is not a user relationship`)
-  }
-
-  let rows = await sdk.rows.fetch(tableId)
+  await sdk.tables.migrate(table, oldColumn, newColumn)
 }

packages/server/src/sdk/app/tables/index.ts

@@ -7,6 +7,7 @@ import {
 } from "../../../integrations/utils"
 import {
   Database,
+  FieldSchema,
   Table,
   TableResponse,
   TableViewsResponse,
@@ -14,6 +15,7 @@ import {
 import datasources from "../datasources"
 import { populateExternalTableSchemas } from "./validation"
 import sdk from "../../../sdk"
+import { migrate } from "./migration"
 
 async function getAllInternalTables(db?: Database): Promise<Table[]> {
   if (!db) {
@@ -84,6 +86,14 @@ async function saveTable(table: Table) {
   }
 }
 
+async function addColumn(table: Table, newColumn: FieldSchema) {
+  if (newColumn.name in table.schema) {
+    throw `Column "${newColumn.name}" already exists on table "${table.name}"`
+  }
+  table.schema[newColumn.name] = newColumn
+  await saveTable(table)
+}
+
 export default {
   getAllInternalTables,
   getAllExternalTables,
@@ -92,4 +102,6 @@ export default {
   populateExternalTableSchemas,
   enrichViewSchemas,
   saveTable,
+  addColumn,
+  migrate,
 }

packages/server/src/sdk/app/tables/migration.ts

@@ -0,0 +1,84 @@
+import { BadRequestError } from "@budibase/backend-core"
+import {
+  BBReferenceFieldMetadata,
+  FieldSchema,
+  InternalTable,
+  RelationshipFieldMetadata,
+  Table,
+  isBBReferenceField,
+  isRelationshipField,
+} from "@budibase/types"
+import { isExternalTable } from "src/integrations/utils"
+import sdk from "../../../sdk"
+
+export async function migrate(
+  table: Table,
+  oldColumn: FieldSchema,
+  newColumn: FieldSchema
+) {
+  let migrator = getColumnMigrator(table, oldColumn, newColumn)
+
+  await sdk.tables.addColumn(table, newColumn)
+
+  migrator.doMigration()
+}
+
+interface ColumnMigrator {
+  doMigration(): Promise<void>
+}
+
+function getColumnMigrator(
+  table: Table,
+  oldColumn: FieldSchema,
+  newColumn: FieldSchema
+): ColumnMigrator {
+  // For now we're only supporting migrations of user relationships to user
+  // columns in internal tables. In future we may want to support other
+  // migrations but for now return an error if we aren't migrating a user
+  // relationship.
+  if (isExternalTable(table._id!)) {
+    throw new BadRequestError("External tables cannot be migrated")
+  }
+
+  if (!(oldColumn.name in table.schema)) {
+    throw new BadRequestError(`Column "${oldColumn.name}" does not exist`)
+  }
+
+  if (newColumn.name in table.schema) {
+    throw new BadRequestError(`Column "${newColumn.name}" already exists`)
+  }
+
+  if (!isBBReferenceField(newColumn)) {
+    throw new BadRequestError(`Column "${newColumn.name}" is not a user column`)
+  }
+
+  if (newColumn.subtype !== "user" && newColumn.subtype !== "users") {
+    throw new BadRequestError(`Column "${newColumn.name}" is not a user column`)
+  }
+
+  if (!isRelationshipField(oldColumn)) {
+    throw new BadRequestError(
+      `Column "${oldColumn.name}" is not a user relationship`
+    )
+  }
+
+  if (oldColumn.tableId !== InternalTable.USER_METADATA) {
+    throw new BadRequestError(
+      `Column "${oldColumn.name}" is not a user relationship`
+    )
+  }
+
+  return new UserColumnMigrator(table, oldColumn, newColumn)
+}
+
+class UserColumnMigrator implements ColumnMigrator {
+  constructor(
+    private table: Table,
+    private oldColumn: RelationshipFieldMetadata,
+    private newColumn: BBReferenceFieldMetadata
+  ) {}
+
+  async doMigration() {
+    let rows = await sdk.rows.fetch(this.table._id!)
+  }
+}