From 2cc26eca0685e41b74da460f4fa2bcf6933a52e9 Mon Sep 17 00:00:00 2001
From: Sander Mertens <sander.mertens8@gmail.com>
Date: Tue, 19 Apr 2022 08:45:50 +0200
Subject: [PATCH] #124 add relationship component query examples

---
 .../c/relations/relation_component/src/main.c | 29 +++++++++++++++----
 .../relations/relation_component/src/main.cpp | 12 ++++++++
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/examples/c/relations/relation_component/src/main.c b/examples/c/relations/relation_component/src/main.c
index 01d1f3cf75..e264850946 100644
--- a/examples/c/relations/relation_component/src/main.c
+++ b/examples/c/relations/relation_component/src/main.c
@@ -34,13 +34,13 @@ int main(int argc, char *argv[]) {
     ecs_entity_t e1 = ecs_new_id(ecs);
     ecs_set_pair(ecs, e1, Requires, Gigawatts, {1.21});
     const Requires *r = ecs_get_pair(ecs, e1, Requires, Gigawatts);
-    printf("requires: %f\n", r->amount);
+    printf("requires: %.2f\n", r->amount);
 
     // The component can be either the first or second part of a pair:
     ecs_entity_t e2 = ecs_new_id(ecs);
     ecs_set_pair_second(ecs, e2, Gigawatts, Requires, {1.21});
     r = ecs_get_pair_second(ecs, e2, Gigawatts, Requires);
-    printf("requires: %f\n", r->amount);
+    printf("requires: %.2f\n", r->amount);
 
     // Note that <Requires, Gigawatts> and <Gigawatts, Requires> are two 
     // different pairs, and can be added to an entity at the same time.
@@ -50,7 +50,7 @@ int main(int argc, char *argv[]) {
     ecs_entity_t e3 = ecs_new_id(ecs);
     ecs_set_pair(ecs, e3, Expires, ecs_id(Position), {0.5});
     const Expires *e = ecs_get_pair(ecs, e3, Expires, ecs_id(Position));
-    printf("expires: %f\n", e->timeout);
+    printf("expires: %.1f\n", e->timeout);
 
     // You can prevent a pair from assuming the type of a component by adding
     // the Tag property to a relationship:
@@ -84,12 +84,29 @@ int main(int argc, char *argv[]) {
     printf("%s\n", type_str);
     ecs_os_free(type_str);
 
+    // When querying for a relationship, provide both parts of the pair:
+    ecs_query_t *q = ecs_query_init(ecs, &(ecs_query_desc_t) {
+        .filter.terms = {
+            { .id = ecs_pair(ecs_id(Requires), Gigawatts) }
+        }
+    });
+
+    // When iterating, always use the pair type:
+    ecs_iter_t it = ecs_query_iter(ecs, q);
+    while (ecs_query_next(&it)) {
+        r = ecs_term(&it, Requires, 1);
+        for (int i = 0; i < it.count; i ++) {
+            printf("requires %.2f gigawatts\n", r[i].amount);
+        }
+    }
+
     // Output:
-    //  requires: 1.210000
-    //  requires: 1.210000
-    //  expires: 0.500000
+    //  requires: 1.21
+    //  requires: 1.21
+    //  expires: 0.5
     //  Requires
     //  Requires
     //  Expires
     //  0
+    //  requires 1.21 gigawatts
 }
diff --git a/examples/cpp/relations/relation_component/src/main.cpp b/examples/cpp/relations/relation_component/src/main.cpp
index 696cad2f93..e532433297 100644
--- a/examples/cpp/relations/relation_component/src/main.cpp
+++ b/examples/cpp/relations/relation_component/src/main.cpp
@@ -60,6 +60,17 @@ int main(int, char*[]) {
     std::cout << ecs.pair<Expires, Position>().type_id().path() << "\n";
     std::cout << ecs.pair<MustHave, Position>().type_id().path() << "\n";
 
+    // When querying for a relationship component, add the pair type as template
+    // argument to the builder:
+    auto q = ecs.query_builder<Requires>()
+        .arg(1).obj<Gigawatts>() // set second part of pair for first term
+        .build();
+    
+    // When iterating, always use the pair type:
+    q.each([](Requires& rq) {
+        std::cout << "requires " << rq.amount << " gigawatts\n";
+    });
+
     // Output:
     //  requires: 1.21
     //  requires: 1.21
@@ -68,4 +79,5 @@ int main(int, char*[]) {
     //  ::Requires
     //  ::Expires
     //  0
+    //  requires 1.21 gigawatts
 }