Example of how to put, query and remove many-to-many database relations using ObjectBox C API

CBoxTest_box_relations.cpp

TEST_CASE("C-Box-relations", "") {
    CTestEnv env;

    env.enableManyEntity();

    obx_schema_id test_id = obx_store_entity_id(env.store(), "TestEntityCpp");

    obx_id ta_id = env.putTestEntity(0, "ta");
    obx_id tb_id = env.putTestEntity(0, "tb");
    obx_id tc_id = env.putTestEntity(0, "tc");
    REQUIRE(ta_id == 1);

    obx_schema_id many_id = obx_store_entity_id(env.store(), "ManyEntityCpp");
    OBX_box* manyBox = obx_box(env.store(), many_id);

    // skip the first 3 so that the IDs don't overlap
    // NOTE rel_put doesn't validate if the src/target ID exists now but it may in the future
    // so having distinct IDs would help ensure the tests are good

    env.putManyEntity(0, "");
    env.putManyEntity(0, "");
    env.putManyEntity(0, "");
    env.txSuccess();
    REQUIRE_OBX_OK(obx_box_remove_all(manyBox, nullptr));

    obx_id ma_id = env.putManyEntity(0, "ma");
    obx_id mb_id = env.putManyEntity(0, "mb");
    obx_id mc_id = env.putManyEntity(0, "mc");
    env.txSuccess();
    REQUIRE(ma_id == 4);

    // Put relations: 3 from "ma", and from "mb" to "tb"
    REQUIRE(obx_box_rel_put(manyBox, 1, ma_id, ta_id) == OBX_SUCCESS);
    REQUIRE(obx_box_rel_put(manyBox, 1, ma_id, tb_id) == OBX_SUCCESS);
    REQUIRE(obx_box_rel_put(manyBox, 1, ma_id, tc_id) == OBX_SUCCESS);
    REQUIRE(obx_box_rel_put(manyBox, 1, mb_id, tb_id) == OBX_SUCCESS);

    // Verify regular direction from "ma"
    OBX_id_array* data0 = obx_box_rel_get_ids(env.box(), env.manyRelationId(), ma_id);
    REQUIRE(data0);
    REQUIRE(data0->count == 3);
    REQUIRE(data0->ids[0] == ta_id);
    REQUIRE(data0->ids[1] == tb_id);
    REQUIRE(data0->ids[2] == tc_id);
    obx_id_array_free(data0);

    // Verify backlink direction from "tb"
    OBX_id_array* dataBack = obx_box_rel_get_backlink_ids(manyBox, env.manyRelationId(), tb_id);
    REQUIRE(dataBack);
    REQUIRE(dataBack->count == 2);
    REQUIRE(dataBack->ids[0] == ma_id);
    REQUIRE(dataBack->ids[1] == mb_id);
    obx_id_array_free(dataBack);

    // Remove one relation (from "ma" to "tb") and test updated regular results from "ma"
    obx_box_rel_remove(manyBox, 1, ma_id, tb_id);
    OBX_id_array* data1 = obx_box_rel_get_ids(env.box(), env.manyRelationId(), ma_id);
    REQUIRE(data1);
    REQUIRE(data1->count == 2);
    REQUIRE(data1->ids[0] == ta_id);
    REQUIRE(data1->ids[1] == tc_id);
    obx_id_array_free(data1);

    // Verify updated backlink direction from "tb" to "mb"
    dataBack = obx_box_rel_get_backlink_ids(manyBox, env.manyRelationId(), tb_id);
    REQUIRE(dataBack);
    REQUIRE(dataBack->count == 1);
    REQUIRE(dataBack->ids[0] == mb_id);
    obx_id_array_free(dataBack);
}