ENH: Add datatypes and value classes to Extern C interface

Summary

See https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/420. Adapts the

Focus

The single get_value functions are now split up into get_<datatype>_value, get_value_list_length, and get_<datatype>_list_value_at functions. Also, importances, roles, and datatypes are now cast from string to enums and back for getting and setting. In the case of datatypes, two additional Booleans for is_reference and is_list.

In addition, the way memory si allocated in case of char pointers has been fixed.

Test Environment

Unit tests and integration tests should be sufficient. Integration testing with deploy in f-grpc and server in f-grpc-f-consolidation, as usual.

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

test/test_ccaosdb.cpp

@@ -184,8 +184,7 @@ TEST_F(test_ccaosdb, test_entity) {
   return_code = caosdb_entity_entity_get_double_value(&entity, value);
   std::cout << *value << std::endl;
   EXPECT_EQ(return_code, 0);
-  // TODO(fspreck) Re-enable once role and datatype are set
-  // EXPECT_EQ(*value, 5.0);
+  EXPECT_EQ(*value, 5.0);
 
   return_code = caosdb_entity_delete_entity(&entity);
   EXPECT_EQ(return_code, 0);
@@ -242,16 +241,13 @@ TEST_F(test_ccaosdb, test_property) {
   caosdb_entity_property_get_unit(&property, &out);
   EXPECT_EQ(strcmp(out, "some_unit"), 0);
 
-  // TODO(fspreck)
-  // caosdb_entity_property_get_string_value(&property, out);
-  // EXPECT_EQ(strcmp(out, "some_value"), 0);
+  caosdb_entity_property_get_string_value(&property, &out);
+  EXPECT_EQ(strcmp(out, "some_value"), 0);
 
   return_code = caosdb_entity_delete_property(&property);
   EXPECT_EQ(return_code, 0);
 }
 
-// TODO(fspreck) Test a property with datatype LIST<Something> and a
-// list value.
 TEST_F(test_ccaosdb, test_list_property) {
 
   caosdb_entity_property property;