expand_foreign_keys() no longer uses inspect, refs #420

datasette/app.py

@@ -29,6 +29,7 @@ from .utils import (
     Results,
     escape_css_string,
     escape_sqlite,
+    get_outbound_foreign_keys,
     get_plugins,
     module_from_path,
     sqlite3,
@@ -464,11 +465,39 @@ class Datasette:
             for p in ps
         ]
 
+    def table_metadata(self, database, table):
+        "Fetch table-specific metadata."
+        return (self.metadata("databases") or {}).get(database, {}).get(
+            "tables", {}
+        ).get(
+            table, {}
+        )
+
     async def table_columns(self, db_name, table):
         return await self.execute_against_connection_in_thread(
             db_name, lambda conn: table_columns(conn, table)
         )
 
+    async def foreign_keys_for_table(self, database, table):
+        return await self.execute_against_connection_in_thread(
+            database, lambda conn: get_outbound_foreign_keys(conn, table)
+        )
+
+    async def label_column_for_table(self, db_name, table):
+        explicit_label_column = (
+            self.table_metadata(
+                db_name, table
+            ).get("label_column")
+        )
+        if explicit_label_column:
+            return explicit_label_column
+        # If a table has two columns, one of which is ID, then label_column is the other one
+        column_names = await self.table_columns(db_name, table)
+        if (column_names and len(column_names) == 2 and "id" in column_names):
+            return [c for c in column_names if c != "id"][0]
+        # Couldn't find a label:
+        return None
+
     async def execute_against_connection_in_thread(self, db_name, fn):
         def in_thread():
             conn = getattr(connections, db_name, None)

datasette/inspect.py

@@ -31,17 +31,6 @@ def inspect_views(conn):
     return [v[0] for v in conn.execute('select name from sqlite_master where type = "view"')]
 
 
-def detect_label_column(column_names):
-    """ Detect the label column - which we display as the label for a joined column.
-
-        If a table has two columns, one of which is ID, then label_column is the other one.
-    """
-    if (column_names and len(column_names) == 2 and "id" in column_names):
-        return [c for c in column_names if c != "id"][0]
-
-    return None
-
-
 def detect_primary_keys(conn, table):
     " Figure out primary keys for a table. "
     table_info_rows = [
@@ -86,7 +75,6 @@ def inspect_tables(conn, database_metadata):
             "columns": column_names,
             "primary_keys": detect_primary_keys(conn, table),
             "count": count,
-            "label_column": detect_label_column(column_names),
             "hidden": table_metadata.get("hidden") or False,
             "fts_table": detect_fts(conn, table),
         }

datasette/utils.py

@@ -475,6 +475,22 @@ def temporary_heroku_directory(
         os.chdir(saved_cwd)
 
 
+def get_outbound_foreign_keys(conn, table):
+    infos = conn.execute(
+        'PRAGMA foreign_key_list([{}])'.format(table)
+    ).fetchall()
+    fks = []
+    for info in infos:
+        if info is not None:
+            id, seq, table_name, from_, to_, on_update, on_delete, match = info
+            fks.append({
+                'other_table': table_name,
+                'column': from_,
+                'other_column': to_
+            })
+    return fks
+
+
 def get_all_foreign_keys(conn):
     tables = [r[0] for r in conn.execute('select name from sqlite_master where type="table"')]
     table_to_foreign_keys = {}

datasette/views/base.py

@@ -131,14 +131,6 @@ class BaseView(RenderMixin):
     def __init__(self, datasette):
         self.ds = datasette
 
-    def table_metadata(self, database, table):
-        "Fetch table-specific metadata."
-        return (self.ds.metadata("databases") or {}).get(database, {}).get(
-            "tables", {}
-        ).get(
-            table, {}
-        )
-
     def options(self, request, *args, **kwargs):
         r = response.text("ok")
         if self.ds.cors:

datasette/views/table.py

@@ -33,7 +33,7 @@ LINK_WITH_VALUE = '<a href="/{database}/{table}/{link_id}">{id}</a>'
 class RowTableShared(BaseView):
 
     async def sortable_columns_for_table(self, database, table, use_rowid):
-        table_metadata = self.table_metadata(database, table)
+        table_metadata = self.ds.table_metadata(database, table)
         if "sortable_columns" in table_metadata:
             sortable_columns = set(table_metadata["sortable_columns"])
         else:
@@ -51,7 +51,7 @@ class RowTableShared(BaseView):
         expandables = []
         for fk in table_info["foreign_keys"]["outgoing"]:
             label_column = (
-                self.table_metadata(
+                self.ds.table_metadata(
                     database, fk["other_table"]
                 ).get("label_column")
                 or tables.get(fk["other_table"], {}).get("label_column")
@@ -62,11 +62,7 @@ class RowTableShared(BaseView):
     async def expand_foreign_keys(self, database, table, column, values):
         "Returns dict mapping (column, value) -> label"
         labeled_fks = {}
-        tables_info = self.ds.inspect()[database]["tables"]
-        table_info = tables_info.get(table) or {}
-        if not table_info:
-            return {}
-        foreign_keys = table_info["foreign_keys"]["outgoing"]
+        foreign_keys = await self.ds.foreign_keys_for_table(database, table)
         # Find the foreign_key for this column
         try:
             fk = [
@@ -75,13 +71,7 @@ class RowTableShared(BaseView):
             ][0]
         except IndexError:
             return {}
-        label_column = (
-            # First look in metadata.json for this foreign key table:
-            self.table_metadata(
-                database, fk["other_table"]
-            ).get("label_column")
-            or tables_info.get(fk["other_table"], {}).get("label_column")
-        )
+        label_column = await self.ds.label_column_for_table(database, fk["other_table"])
         if not label_column:
             return {
                 (fk["column"], value): str(value)
@@ -119,7 +109,7 @@ class RowTableShared(BaseView):
         truncate_cells=0,
     ):
         "Returns columns, rows for specified table - including fancy foreign key treatment"
-        table_metadata = self.table_metadata(database, table)
+        table_metadata = self.ds.table_metadata(database, table)
         info = self.ds.inspect()[database]
         sortable_columns = await self.sortable_columns_for_table(database, table, True)
         columns = [
@@ -309,7 +299,7 @@ class TableView(RowTableShared):
                 forward_querystring=False,
             )
 
-        table_metadata = self.table_metadata(database, table)
+        table_metadata = self.ds.table_metadata(database, table)
         units = table_metadata.get("units", {})
         filters = Filters(sorted(other_args.items()), units, ureg)
         where_clauses, params = filters.build_where_clauses()
@@ -880,7 +870,7 @@ class RowView(RowTableShared):
             "columns": columns,
             "primary_keys": pks,
             "primary_key_values": pk_values,
-            "units": self.table_metadata(database, table).get("units", {}),
+            "units": self.ds.table_metadata(database, table).get("units", {}),
         }
 
         if "foreign_key_tables" in (request.raw_args.get("_extras") or "").split(","):