feat: add generic types to .select()

README.md

@@ -22,7 +22,20 @@ import 'package:postgrest/postgrest.dart';
 
 final url = 'https://example.com/postgrest/endpoint';
 final client = PostgrestClient(url);
-final response = await client.from('users').select();
+final response = await client.from<PostgrestList>('users').select();
+```
+
+#### Reading your data and converting it to an object
+
+```dart
+import 'package:postgrest/postgrest.dart';
+
+final url = 'https://example.com/postgrest/endpoint';
+final client = PostgrestClient(url);
+final response = await client
+    .from('users')
+    .select<PostgrestList>()
+    .withConverter((data) => data.map(User.fromJson).toList());
 ```
 
 #### Insert records
@@ -33,7 +46,7 @@ import 'package:postgrest/postgrest.dart';
 final url = 'https://example.com/postgrest/endpoint';
 final client = PostgrestClient(url);
 try {
-  final data = await client.from('users')
+  await client.from('users')
     .insert([
       {'username': 'supabot', 'status': 'ONLINE'}
     ]);
@@ -53,7 +66,7 @@ import 'package:postgrest/postgrest.dart';
 
 final url = 'https://example.com/postgrest/endpoint';
 final client = PostgrestClient(url);
-final data = await client.from('users')
+await client.from('users')
       .update({'status': 'OFFLINE'})
       .eq('username', 'dragarcia');
 ```
@@ -65,7 +78,7 @@ import 'package:postgrest/postgrest.dart';
 
 final url = 'https://example.com/postgrest/endpoint';
 final client = PostgrestClient(url);
-final data = await client.from('users')
+await client.from('users')
       .delete()
       .eq('username', 'supabot');
 ```
@@ -78,7 +91,7 @@ import 'package:postgrest/postgrest.dart';
 final url = 'https://example.com/postgrest/endpoint';
 final client = PostgrestClient(url);
 final response = await client.from('countries')
-      .select('*', FetchOptions(count: CountOption.exact));
+      .select<PostgrestResponse>('*', FetchOptions(count: CountOption.exact));
 final data = response.data;
 final count = response.count;
 ```

lib/src/postgrest.dart

@@ -32,9 +32,9 @@ class PostgrestClient {
   }
 
   /// Perform a table operation.
-  PostgrestQueryBuilder from(String table) {
+  PostgrestQueryBuilder<void> from(String table) {
     final url = '${this.url}/$table';
-    return PostgrestQueryBuilder(
+    return PostgrestQueryBuilder<void>(
       url,
       headers: headers,
       schema: schema,

lib/src/postgrest_builder.dart

@@ -23,15 +23,17 @@ const METHOD_PUT = 'PUT';
 const METHOD_PATCH = 'PATCH';
 const METHOD_DELETE = 'DELETE';
 
+typedef _Nullable<T> = T?;
+
 /// The base builder class.
-class PostgrestBuilder<T> implements Future<T?> {
+class PostgrestBuilder<T, S> implements Future<T> {
   dynamic _body;
   late final Headers _headers;
   bool _maybeEmpty = false;
   String? _method;
   late final String? _schema;
   late Uri _url;
-  PostgrestConverter? _converter;
+  PostgrestConverter<T, S>? _converter;
   late final Client? _httpClient;
   // ignore: prefer_final_fields
   FetchOptions? _options;
@@ -62,9 +64,8 @@ class PostgrestBuilder<T> implements Future<T?> {
   ///     .select()
   ///     .withConverter<User>((data) => User.fromJson(data));
   /// ```
-  PostgrestBuilder<S> withConverter<S>(PostgrestConverter<S> converter) {
-    _converter = converter;
-    return PostgrestBuilder<S>(
+  PostgrestBuilder<R, T> withConverter<R>(PostgrestConverter<R, T> converter) {
+    return PostgrestBuilder<R, T>(
       url: _url,
       headers: _headers,
       schema: _schema,
@@ -75,6 +76,22 @@ class PostgrestBuilder<T> implements Future<T?> {
       .._converter = converter;
   }
 
+  void _assertCorrectGeneric(Type R) {
+    assert(
+        R == PostgrestList ||
+            R == PostgrestMap ||
+            R == (_Nullable<PostgrestMap>) ||
+            R == PostgrestListResponse ||
+            R == PostgrestMapResponse ||
+            R == (PostgrestResponse<PostgrestMap?>) ||
+            R == PostgrestResponse ||
+            R == List ||
+            R == (List<Map>) ||
+            R == Map ||
+            R == dynamic,
+        "$R is not allowed as generic for `select<R>()`. Allowed types are: `PostgrestList`, `PostgrestMap`, `PostgrestMap?`, `PostgrestListResponse`, `PostgrestMapResponse`, `PostgrestResponse`, `dynamic`.");
+  }
+
   /// Sends the request and returns a [PostgrestResponse]
   ///
   /// [head] to trigger a HEAD request
@@ -92,7 +109,7 @@ class PostgrestBuilder<T> implements Future<T?> {
   /// }
   /// ```
   @Deprecated('Use async/await or .then instead. Deprecated in 0.2.0')
-  Future<PostgrestResponse<T>> execute({
+  Future<PostgrestResponse> execute({
     bool head = false,
     CountOption? count,
   }) async {
@@ -103,7 +120,7 @@ class PostgrestBuilder<T> implements Future<T?> {
     return _execute();
   }
 
-  Future<PostgrestResponse<T>> _execute() async {
+  Future<PostgrestResponse> _execute() async {
     if (_options?.head ?? false) {
       _method = METHOD_HEAD;
     }
@@ -183,7 +200,7 @@ class PostgrestBuilder<T> implements Future<T?> {
   }
 
   /// Parse request response to json object if possible
-  Future<PostgrestResponse<T>> _parseResponse(http.Response response) async {
+  Future<PostgrestResponse> _parseResponse(http.Response response) async {
     if (response.statusCode >= 200 && response.statusCode <= 299) {
       dynamic body;
       int? count;
@@ -207,12 +224,62 @@ class PostgrestBuilder<T> implements Future<T?> {
             : int.parse(contentRange.split('/').last);
       }
 
+      // When using converter [S] is the type of the converter functions's argument. Otherwise [T] should be equal to [S]
+      if (S == PostgrestList) {
+        body = PostgrestList.from(body as Iterable) as S;
+      } else if (S == List<Map>) {
+        body = List<Map>.from(body as Iterable) as S;
+      } else if (S == PostgrestMap) {
+        body = PostgrestMap.from(body as Map) as S;
+
+        //You can't write `S == PostgrestMap?`
+      } else if (S == _Nullable<PostgrestMap>) {
+        if (body == null) {
+          body = null as S;
+        } else {
+          body = PostgrestMap.from(body as Map) as S;
+        }
+      } else if (S == PostgrestListResponse) {
+        body = PostgrestList.from(body as Iterable);
+        if (_converter != null) {
+          body = _converter!(body as S);
+        }
+        return PostgrestResponse<PostgrestList>(
+          data: body,
+          status: response.statusCode,
+          count: count,
+        );
+      } else if (S == PostgrestMapResponse) {
+        body = PostgrestMap.from(body as Map);
+        if (_converter != null) {
+          body = _converter!(body as S);
+        }
+        return PostgrestResponse<PostgrestMap>(
+          data: body,
+          status: response.statusCode,
+          count: count,
+        );
+      } else if (S == PostgrestResponse<PostgrestMap?>) {
+        if (body == null) {
+          body = null;
+        } else {
+          body = PostgrestMap.from(body as Map);
+        }
+        if (_converter != null) {
+          body = _converter!(body as S);
+        }
+        return PostgrestResponse<PostgrestMap?>(
+          data: body,
+          status: response.statusCode,
+          count: count,
+        );
+      }
       if (_converter != null) {
         body = _converter!(body);
       }
 
-      return PostgrestResponse<T>(
-        data: body as T,
+      return PostgrestResponse(
+        data: body,
         status: response.statusCode,
         count: count,
       );
@@ -289,8 +356,8 @@ class PostgrestBuilder<T> implements Future<T?> {
   }
 
   @override
-  Stream<T?> asStream() {
-    final controller = StreamController<T?>.broadcast();
+  Stream<T> asStream() {
+    final controller = StreamController<T>.broadcast();
 
     then((value) {
       controller.add(value);
@@ -311,7 +378,7 @@ class PostgrestBuilder<T> implements Future<T?> {
   /// Register callbacks to be called when this future completes.
   @override
   Future<R> then<R>(
-    FutureOr<R> Function(T? value) onValue, {
+    FutureOr<R> Function(T value) onValue, {
     Function? onError,
   }) async {
     if (onError != null &&
@@ -378,7 +445,7 @@ class PostgrestBuilder<T> implements Future<T?> {
   }
 
   @override
-  Future<T?> whenComplete(FutureOr<void> Function() action) {
+  Future<T> whenComplete(FutureOr<void> Function() action) {
     return then(
       (v) {
         final f2 = action();