Rough prototype of cross-database-joins, refs #283

This is a quick-and-dirty proof of concept.

datasette/templates/database.html

@@ -16,7 +16,7 @@
 
 {% block description_source_license %}{% include "_description_source_license.html" %}{% endblock %}
 
-<form class="sql" action="/{{ database }}-{{ database_hash }}" method="get">
+<form class="sql" action="/{{ database }}{% if database_hash %}-{{ database_hash }}{% endif %}" method="get">
     <h3>Custom SQL query</h3>
     <p><textarea name="sql">select * from {{ tables[0].name|escape_sqlite }}</textarea></p>
     <p><input type="submit" value="Run SQL"></p>

datasette/templates/query.html

@@ -23,7 +23,7 @@
 
 <h1 style="padding-left: 10px; border-left: 10px solid #{{ database_hash[:6] }}">{{ database }}</h1>
 
-<form class="sql" action="/{{ database }}-{{ database_hash }}{% if canned_query %}/{{ canned_query }}{% endif %}" method="get">
+<form class="sql" action="/{{ database }}{% if database_hash %}-{{ database_hash }}{% endif %}{% if canned_query %}/{{ canned_query }}{% endif %}" method="get">
     <h3>Custom SQL query{% if rows %} returning {% if truncated %}more than {% endif %}{{ "{:,}".format(rows|length) }} row{% if rows|length == 1 %}{% else %}s{% endif %}{% endif %}</h3>
     {% if editable %}
         <p><textarea name="sql">{% if query and query.sql %}{{ query.sql }}{% else %}select * from {{ tables[0].name|escape_sqlite }}{% endif %}</textarea></p>

datasette/views/base.py

@@ -107,6 +107,8 @@ class BaseView(RenderMixin):
                 hash = None
         else:
             name = db_name
+        if name == "memory":
+            return "memory", "", None
         # Verify the hash
         try:
             info = databases[name]
@@ -143,14 +145,25 @@ class BaseView(RenderMixin):
         def sql_operation_in_thread():
             conn = getattr(connections, db_name, None)
             if not conn:
-                info = self.ds.inspect()[db_name]
+                if db_name == "memory":
+                    filename = ":memory:"
+                else:
+                    info = self.ds.inspect()[db_name]
+                    filename = info["file"]
                 conn = sqlite3.connect(
-                    "file:{}?immutable=1".format(info["file"]),
+                    "file:{}?immutable=1".format(filename),
                     uri=True,
                     check_same_thread=False,
                 )
                 self.ds.prepare_connection(conn)
                 setattr(connections, db_name, conn)
+                if db_name == "memory":
+                    # Loop through and attach all the other DBs
+                    for dbname, dbinfo in self.ds.inspect().items():
+                        sql2 = 'ATTACH DATABASE "file:{}?immutable=1" AS [{}];'.format(
+                            dbinfo["file"], dbname
+                        )
+                        conn.execute(sql2)
 
             time_limit_ms = self.ds.sql_time_limit_ms
             if custom_time_limit and custom_time_limit < self.ds.sql_time_limit_ms:

datasette/views/database.py

@@ -15,7 +15,17 @@ class DatabaseView(BaseView):
             validate_sql_select(sql)
             return await self.custom_sql(request, name, hash, sql)
 
-        info = self.ds.inspect()[name]
+        if name == "memory":
+            info = {"tables": {
+                "sqlite_master": {
+                    "name": "sqlite_master",
+                    "hidden": False,
+                    "columns": [],
+                    "count": 0,
+                }
+            }, "views": []}
+        else:
+            info = self.ds.inspect()[name]
         metadata = self.ds.metadata.get("databases", {}).get(name, {})
         self.ds.update_with_inherited_metadata(metadata)
         tables = list(info["tables"].values())