label_column option in metadata.json - closes #234

datasette/app.py

@@ -524,7 +524,12 @@ class RowTableShared(BaseView):
         if table_info and expand_foreign_keys:
             foreign_keys = table_info['foreign_keys']['outgoing']
             for fk in foreign_keys:
-                label_column = tables.get(fk['other_table'], {}).get('label_column')
+                label_column = (
+                    # First look for metadata.json definition:
+                    table_metadata.get('label_column')
+                    # Fall back to label_column from .inspect() detection:
+                    or tables.get(fk['other_table'], {}).get('label_column')
+                )
                 if not label_column:
                     # No label for this FK
                     fks[fk['column']] = fk['other_table']

docs/metadata.rst

@@ -81,7 +81,7 @@ Column units are configured in the metadata like so::
 Units are interpreted using Pint_, and you can see the full list of available units in
 Pint's `unit registry`_. You can also add `custom units`_ to the metadata, which will be
 registered with Pint::
-    
+
     {
         "custom_units": [
             "decibel = [] = dB"
@@ -119,6 +119,29 @@ This will restrict sorting of ``example_table`` to just the ``height`` and
 
 You can also disable sorting entirely by setting ``"sortable_columns": []``
 
+Specifying the label column for a table
+---------------------------------------
+
+Datasette's HTML interface attempts to display foreign key references as
+labelled hyperlinks. By default, it looks for referenced tables that only have
+two columns: a primary key column and one other. It assumes that the second
+column should be used as the link label.
+
+If your table has more than two columns you can specify which column should be
+used for the link label with the ``label_column`` property::
+
+    {
+        "databases": {
+            "database1": {
+                "tables": {
+                    "example_table": {
+                        "label_column": "title"
+                    }
+                }
+            }
+        }
+    }
+
 Generating a metadata skeleton
 ------------------------------
 

tests/fixtures.py

@@ -97,6 +97,9 @@ METADATA = {
                         'frequency': 'Hz'
                     }
                 },
+                'custom_foreign_key_label': {
+                    'label_column': 'content2',
+                },
             }
         },
     }
@@ -215,6 +218,12 @@ CREATE TABLE "complex_foreign_keys" (
   FOREIGN KEY ("f3") REFERENCES [simple_primary_key](id)
 );
 
+CREATE TABLE "custom_foreign_key_label" (
+  pk varchar(30) primary key,
+  foreign_key_with_custom_label text,
+  FOREIGN KEY ("foreign_key_with_custom_label") REFERENCES [primary_key_multiple_columns](id)
+);
+
 CREATE TABLE units (
   pk integer primary key,
   distance int,
@@ -241,6 +250,7 @@ INSERT INTO primary_key_multiple_columns VALUES (1, 'hey', 'world');
 INSERT INTO foreign_key_references VALUES (1, 1, 1);
 
 INSERT INTO complex_foreign_keys VALUES (1, 1, 2, 1);
+INSERT INTO custom_foreign_key_label VALUES (1, 1);
 
 INSERT INTO [table/with/slashes.csv] VALUES (3, 'hey');
 

tests/test_api.py

@@ -17,7 +17,7 @@ def test_homepage(app_client):
     assert response.json.keys() == {'test_tables': 0}.keys()
     d = response.json['test_tables']
     assert d['name'] == 'test_tables'
-    assert d['tables_count'] == 13
+    assert d['tables_count'] == 14
 
 
 def test_database_page(app_client):
@@ -80,6 +80,21 @@ def test_database_page(app_client):
         'label_column': None,
         'primary_keys': ['pk1', 'pk2', 'pk3'],
     }, {
+        'columns': ['pk', 'foreign_key_with_custom_label'],
+        'name': 'custom_foreign_key_label',
+        'count': 1,
+        'hidden': False,
+        'foreign_keys': {
+            'incoming': [],
+            'outgoing':  [{
+                'column': 'foreign_key_with_custom_label',
+                'other_column': 'id',
+                'other_table': 'primary_key_multiple_columns'
+            }],
+        },
+        'label_column': None,
+        'primary_keys': ['pk'],
+    },  {
         'columns': ['pk', 'foreign_key_with_label', 'foreign_key_with_no_label'],
         'name': 'foreign_key_references',
         'count': 1,
@@ -115,6 +130,10 @@ def test_database_page(app_client):
                 'column': 'id',
                 'other_column': 'foreign_key_with_no_label',
                 'other_table': 'foreign_key_references'
+            }, {
+                'column': 'id',
+                'other_column': 'foreign_key_with_custom_label',
+                'other_table': 'custom_foreign_key_label'
             }],
             'outgoing': []
         },

tests/test_html.py

@@ -294,6 +294,19 @@ def test_table_html_foreign_key_links(app_client):
     assert expected == [[str(td) for td in tr.select('td')] for tr in table.select('tbody tr')]
 
 
+def test_table_html_foreign_key_custom_label_column(app_client):
+    response = app_client.get('/test_tables/custom_foreign_key_label', gather_request=False)
+    assert response.status == 200
+    table = Soup(response.body, 'html.parser').find('table')
+    expected = [
+        [
+            '<td class="col-pk"><a href="/test_tables/custom_foreign_key_label/1">1</a></td>',
+            '<td class="col-foreign_key_with_custom_label"><a href="/test_tables/primary_key_multiple_columns/1">world</a>\xa0<em>1</em></td>',
+        ]
+    ]
+    assert expected == [[str(td) for td in tr.select('td')] for tr in table.select('tbody tr')]
+
+
 def test_row_html_compound_primary_key(app_client):
     response = app_client.get('/test_tables/compound_primary_key/a,b', gather_request=False)
     assert response.status == 200