Merge branch 'sb/avro_arr'

Closes #48.

Author: Totktonada

README.md

@@ -47,6 +47,44 @@ GraphQL queries on data from the local Tarantool's storage called spaces.
 It is planned to implement another data accessor that allows to fetch objects
 sharded using tarantool/shard module.
 
+### Notes on types
+
+User should distinguish between Object and Map types. Both of them consists of
+keys and values but there are some important differences.
+
+While Object is a GraphQL built-in type, Map is a scalar-based type. In case of
+Object-based type all key-value pairs are set during type definition and values
+may have different types (as defined in the schema).
+
+In contrast, set of valid Map keys is not defined in the schema, any key-value
+pair is valid despite name of the key while value has schema-determined type
+(which is the same among all values in the map).
+
+Map-based types should be queried as a scalar type, not as an object type
+(because map's keys are not part of the schema).
+
+The following example works:
+
+```
+{
+    …
+    map_based_type
+    …
+}
+```
+
+The following example doesn't work:
+
+```
+{
+    …
+    map_based_type {
+        key_1
+    }
+    …
+}
+```
+
 ## Run tests
 
 ```
@@ -57,7 +95,7 @@ make test
 
 ## Requirements
 
-* For use: tarantool, lulpeg, >=tarantool/shard-1.1-91-gfa88bf8 (optional), 
+* For use: tarantool, lulpeg, >=tarantool/shard-1.1-91-gfa88bf8 (optional),
   tarantool/avro-schema.
 * For test (additionally to 'for use'): python 2.7, virtualenv, luacheck.
 * For building apidoc (additionally to 'for use'): ldoc.