Add a way to export SQLAlchemy models from Gel (EdgeDB).

Create separate intermediate objects to represent links with link
properties (because ORMs tend to view them as such).
Don't allow crazy names (not usual type of identifiers).

Multi properties behave more like plain multi links than anything else
(because they have a separate table with the property value in it),
so they should be reflected like that establishing a relationship.

Reflect Gel modules into Python modules.

Add tests that setup a Gel database and then generate the SQLAlchemy
models from it. The individual tests use a SQLAlchemy session to access
the database using postgres protocol.

.flake8

@@ -1,3 +1,3 @@
 [flake8]
 ignore = B008,B023,B306,E203,E402,E731,D100,D101,D102,D103,D104,D105,W503,W504,E252,F999,F541
-exclude = .git,__pycache__,build,dist,.eggs
+exclude = .git,__pycache__,build,dist,.eggs,generated

gel/_testbase.py

@@ -35,6 +35,8 @@
 import gel
 from gel import asyncio_client
 from gel import blocking_client
+from gel.orm.introspection import get_schema_json
+from gel.orm.sqla import ModelGenerator
 
 
 log = logging.getLogger(__name__)
@@ -627,6 +629,46 @@ def adapt_call(cls, result):
         return result
 
 
+class SQLATestCase(SyncQueryTestCase):
+    SQLAPACKAGE = None
+    DEFAULT_MODULE = 'default'
+
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+
+        class_set_up = os.environ.get('EDGEDB_TEST_CASES_SET_UP')
+        if not class_set_up:
+            # Now that the DB is setup, generate the SQLAlchemy models from it
+            spec = get_schema_json(cls.client)
+            # We'll need a temp directory to setup the generated Python
+            # package
+            cls.tmpsqladir = tempfile.TemporaryDirectory()
+            gen = ModelGenerator(
+                outdir=os.path.join(cls.tmpsqladir.name, cls.SQLAPACKAGE),
+                basemodule=cls.SQLAPACKAGE,
+            )
+            gen.render_models(spec)
+            sys.path.append(cls.tmpsqladir.name)
+
+    @classmethod
+    def tearDownClass(cls):
+        super().tearDownClass()
+        # cleanup the temp modules
+        sys.path.remove(cls.tmpsqladir.name)
+        cls.tmpsqladir.cleanup()
+
+    @classmethod
+    def get_dsn_for_sqla(cls):
+        cargs = cls.get_connect_args(database=cls.get_database_name())
+        dsn = (
+            f'postgresql://{cargs["user"]}:{cargs["password"]}'
+            f'@{cargs["host"]}:{cargs["port"]}/{cargs["database"]}'
+        )
+
+        return dsn
+
+
 _lock_cnt = 0
 
 

gel/orm/introspection.py

@@ -0,0 +1,206 @@
+import json
+import re
+
+
+INTRO_QUERY = '''
+with module schema
+select ObjectType {
+    name,
+    links: {
+        name,
+        readonly,
+        required,
+        cardinality,
+        exclusive := exists (
+            select .constraints
+            filter .name = 'std::exclusive'
+        ),
+        target: {name},
+
+        properties: {
+            name,
+            readonly,
+            required,
+            cardinality,
+            exclusive := exists (
+                select .constraints
+                filter .name = 'std::exclusive'
+            ),
+            target: {name},
+        },
+    } filter .name != '__type__',
+    properties: {
+        name,
+        readonly,
+        required,
+        cardinality,
+        exclusive := exists (
+            select .constraints
+            filter .name = 'std::exclusive'
+        ),
+        target: {name},
+    },
+    backlinks := <array<str>>[],
+}
+filter
+    not .builtin
+    and
+    not .internal
+    and
+    not re_test('^(std|cfg|sys|schema)::', .name);
+'''
+
+MODULE_QUERY = '''
+with
+    module schema,
+    m := (select `Module` filter not .builtin)
+select m.name;
+'''
+
+CLEAN_NAME = re.compile(r'^[A-Za-z_][A-Za-z0-9_]*$')
+
+
+def get_sql_name(name):
+    # Just remove the module name
+    name = name.rsplit('::', 1)[-1]
+
+    return name
+
+
+def check_name(name):
+    # Just remove module separators and check the rest
+    name = name.replace('::', '')
+    if not CLEAN_NAME.fullmatch(name):
+        raise RuntimeError(
+            f'Non-alphanumeric names are not supported: {name}')
+
+
+def get_schema_json(client):
+    types = json.loads(client.query_json(INTRO_QUERY))
+    modules = json.loads(client.query_json(MODULE_QUERY))
+
+    return _process_links(types, modules)
+
+
+async def async_get_schema_json(client):
+    types = json.loads(await client.query_json(INTRO_QUERY))
+    modules = json.loads(client.query_json(MODULE_QUERY))
+
+    return _process_links(types, modules)
+
+
+def _process_links(types, modules):
+    # Figure out all the backlinks, link tables, and links with link
+    # properties that require their own intermediate objects.
+    type_map = {}
+    link_tables = []
+    link_objects = []
+    prop_objects = []
+
+    for spec in types:
+        check_name(spec['name'])
+        type_map[spec['name']] = spec
+
+        for prop in spec['properties']:
+            check_name(prop['name'])
+
+    for spec in types:
+        mod = spec["name"].rsplit('::', 1)[0]
+        sql_source = get_sql_name(spec["name"])
+
+        for prop in spec['properties']:
+            exclusive = prop['exclusive']
+            cardinality = prop['cardinality']
+            name = prop['name']
+            check_name(name)
+            sql_name = get_sql_name(name)
+
+            if cardinality == 'Many':
+                # Multi property will make its own "link table". But since it
+                # doesn't link to any other object the link table itself must
+                # be reflected as an object.
+                pobj = {
+                    'module': mod,
+                    'name': f'{sql_source}_{sql_name}_prop',
+                    'table': f'{sql_source}.{sql_name}',
+                    'links': [{
+                        'name': 'source',
+                        'required': True,
+                        'cardinality': 'One' if exclusive else 'Many',
+                        'exclusive': cardinality == 'One',
+                        'target': {'name': spec['name']},
+                        'has_link_object': False,
+                    }],
+                    'properties': [{
+                        'name': 'target',
+                        'required': True,
+                        'cardinality': 'One',
+                        'exclusive': False,
+                        'target': prop['target'],
+                        'has_link_object': False,
+                    }],
+                }
+                prop_objects.append(pobj)
+
+        for link in spec['links']:
+            if link['name'] != '__type__':
+                target = link['target']['name']
+                cardinality = link['cardinality']
+                exclusive = link['exclusive']
+                name = link['name']
+                check_name(name)
+                sql_name = get_sql_name(name)
+
+                objtype = type_map[target]
+                objtype['backlinks'].append({
+                    'name': f'backlink_via_{sql_name}',
+                    # flip cardinality and exclusivity
+                    'cardinality': 'One' if exclusive else 'Many',
+                    'exclusive': cardinality == 'One',
+                    'target': {'name': spec['name']},
+                    'has_link_object': False,
+                })
+
+                for prop in link['properties']:
+                    check_name(prop['name'])
+
+                link['has_link_object'] = False
+                # Any link with properties should become its own intermediate
+                # object, since ORMs generally don't have a special convenient
+                # way of exposing this as just a link table.
+                if len(link['properties']) > 2:
+                    # more than just 'source' and 'target' properties
+                    lobj = {
+                        'module': mod,
+                        'name': f'{sql_source}_{sql_name}_link',
+                        'table': f'{sql_source}.{sql_name}',
+                        'links': [],
+                        'properties': [],
+                    }
+                    for prop in link['properties']:
+                        if prop['name'] in {'source', 'target'}:
+                            lobj['links'].append(prop)
+                        else:
+                            lobj['properties'].append(prop)
+
+                    link_objects.append(lobj)
+                    link['has_link_object'] = True
+                    objtype['backlinks'][-1]['has_link_object'] = True
+
+                elif cardinality == 'Many':
+                    # Add a link table for One-to-Many and Many-to-Many
+                    link_tables.append({
+                        'module': mod,
+                        'name': f'{sql_source}_{sql_name}_table',
+                        'table': f'{sql_source}.{sql_name}',
+                        'source': spec["name"],
+                        'target': target,
+                    })
+
+    return {
+        'modules': modules,
+        'object_types': types,
+        'link_tables': link_tables,
+        'link_objects': link_objects,
+        'prop_objects': prop_objects,
+    }