Improved PaginateConfig and Column autocompletion (#931)

src/helper.ts

@@ -1,36 +1,72 @@
 import { SelectQueryBuilder } from 'typeorm'
 import { ColumnMetadata } from 'typeorm/metadata/ColumnMetadata'
 
+/**
+ * Joins 2 keys as `K`, `K.P`, `K.(P` or `K.P)`
+ * The parenthesis notation is included for embedded columns
+ */
 type Join<K, P> = K extends string
     ? P extends string
         ? `${K}${'' extends P ? '' : '.'}${P | `(${P}` | `${P})`}`
         : never
     : never
 
+/**
+ * Get the previous number between 0 and 10. Examples:
+ *   Prev[3] = 2
+ *   Prev[0] = never.
+ *   Prev[20] = 0
+ */
 type Prev = [never, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ...0[]]
 
-// unwrap Promise type
+/**
+ * Unwrap Promise<T> to T
+ */
 type UnwrapPromise<T> = T extends Promise<infer U> ? UnwrapPromise<U> : T
 
-// Unwrap Array type
+/**
+ * Unwrap Array<T> to T
+ */
 type UnwrapArray<T> = T extends Array<infer U> ? UnwrapArray<U> : T
 
-// TODO: puts some comments here, in this ternary of doom
+/**
+ * Find all the dotted path properties for a given column.
+ *
+ * T: The column
+ * D: max depth
+ */
+//                                            v Have we reached max depth?
 export type Column<T, D extends number = 2> = [D] extends [never]
-    ? never
-    : T extends Record<string, any>
+    ? // yes, stop recursing
+      never
+    : // Are we extending something with keys?
+    T extends Record<string, any>
     ? {
+          // For every keyof T, find all possible properties as a string union
           [K in keyof T]-?: K extends string
-              ? T[K] extends Date
-                  ? `${K}`
-                  : T[K] extends Array<infer U>
-                  ? `${K}` | Join<K, Column<UnwrapArray<U>, Prev[D]>>
-                  : T[K] extends Promise<infer U>
-                  ? U extends Array<infer V>
+              ? // Is it string or number (includes enums)?
+                T[K] extends string | number
+                  ? // yes, add just the key
+                    `${K}`
+                  : // Is it a Date?
+                  T[K] extends Date
+                  ? // yes, add just the key
+                    `${K}`
+                  : // no, is it an array?
+                  T[K] extends Array<infer U>
+                  ? // yes, unwrap it, and recurse deeper
+                    `${K}` | Join<K, Column<UnwrapArray<U>, Prev[D]>>
+                  : // no, is it a promise?
+                  T[K] extends Promise<infer U>
+                  ? // yes, try to infer its return type and recurse
+                    U extends Array<infer V>
                       ? `${K}` | Join<K, Column<UnwrapArray<V>, Prev[D]>>
                       : `${K}` | Join<K, Column<UnwrapPromise<U>, Prev[D]>>
-                  : `${K}` | Join<K, Column<T[K], Prev[D]>>
+                  : // no, we have no more special cases, so treat it as an
+                    // object and recurse deeper on its keys
+                    `${K}` | Join<K, Column<T[K], Prev[D]>>
               : never
+          // Join all the string unions of each keyof T into a single string union
       }[keyof T]
     : ''
 

src/paginate.ts

@@ -70,13 +70,17 @@ export interface PaginateConfig<T> {
     sortableColumns: Column<T>[]
     nullSort?: 'first' | 'last'
     searchableColumns?: Column<T>[]
-    select?: Column<T>[] | string[]
+    // see https://github.com/microsoft/TypeScript/issues/29729 for (string & {})
+    // eslint-disable-next-line @typescript-eslint/ban-types
+    select?: (Column<T> | (string & {}))[]
     maxLimit?: number
     defaultSortBy?: SortBy<T>
     defaultLimit?: number
     where?: FindOptionsWhere<T> | FindOptionsWhere<T>[]
     filterableColumns?: {
-        [key in Column<T> | string]?: (FilterOperator | FilterSuffix)[] | true
+        // see https://github.com/microsoft/TypeScript/issues/29729 for (string & {})
+        // eslint-disable-next-line @typescript-eslint/ban-types
+        [key in Column<T> | (string & {})]?: (FilterOperator | FilterSuffix)[] | true
     }
     loadEagerRelations?: boolean
     withDeleted?: boolean