?_labels= and ?_label=COL to expand foreign keys in JSON/CSV

These new querystring arguments can be used to request expanded foreign keys
in both JSON and CSV formats.

?_labels=on turns on expansions for ALL foreign key columns

?_label=COLUMN1&_label=COLUMN2 can be used to pick specific columns to expand

e.g. `Street_Tree_List.json?_label=qSpecies&_label=qLegalStatus`

    {
        "rowid": 233,
        "TreeID": 121240,
        "qLegalStatus": {
            "value" 2,
            "label": "Private"
        }
        "qSpecies": {
            "value": 16,
            "label": "Sycamore"
        }
        "qAddress": "91 Commonwealth Ave",
        ...
    }

The labels option also works for the HTML and CSV views.

HTML defaults to `?_labels=on`, so if you pass `?_labels=off` you can disable
foreign key expansion entirely - or you can use `?_label=COLUMN` to request
just specific columns.

If you expand labels on CSV you get additional columns in the output:

`/Street_Tree_List.csv?_label=qLegalStatus`

    rowid,TreeID,qLegalStatus,qLegalStatus_label...
    1,141565,1,Permitted Site...
    2,232565,2,Undocumented...

I also refactored the existing foreign key expansion code.

Closes #233. Refs #266.

tests/test_api.py

@@ -1096,6 +1096,52 @@ def test_suggest_facets_off():
         ).json["suggested_facets"]
 
 
+def test_expand_labels(app_client):
+    response = app_client.get(
+        "/test_tables/facetable.json?_shape=object&_labels=1&_size=2"
+        "&neighborhood__contains=c"
+    )
+    assert {
+        "2": {
+            "pk": 2,
+            "planet_int": 1,
+            "state": "CA",
+            "city_id": {
+                "value": 1,
+                "label": "San Francisco"
+            },
+            "neighborhood": "Dogpatch"
+        },
+        "13": {
+            "pk": 13,
+            "planet_int": 1,
+            "state": "MI",
+            "city_id": {
+                "value": 3,
+                "label": "Detroit"
+            },
+            "neighborhood": "Corktown"
+        }
+    } == response.json
+
+
+def test_expand_label(app_client):
+    response = app_client.get(
+        "/test_tables/foreign_key_references.json?_shape=object"
+        "&_label=foreign_key_with_label"
+    )
+    assert {
+        "1": {
+            "pk": "1",
+            "foreign_key_with_label": {
+                "value": "1",
+                "label": "hello"
+            },
+            "foreign_key_with_no_label": "1"
+        }
+    } == response.json
+
+
 @pytest.mark.parametrize('path,expected_cache_control', [
     ("/test_tables/facetable.json", "max-age=31536000"),
     ("/test_tables/facetable.json?_ttl=invalid", "max-age=31536000"),

tests/test_csv.py

@@ -11,6 +11,24 @@ hello
 world
 '''.replace('\n', '\r\n')
 
+EXPECTED_TABLE_WITH_LABELS_CSV = '''
+pk,planet_int,state,city_id,city_id_label,neighborhood
+1,1,CA,1,San Francisco,Mission
+2,1,CA,1,San Francisco,Dogpatch
+3,1,CA,1,San Francisco,SOMA
+4,1,CA,1,San Francisco,Tenderloin
+5,1,CA,1,San Francisco,Bernal Heights
+6,1,CA,1,San Francisco,Hayes Valley
+7,1,CA,2,Los Angeles,Hollywood
+8,1,CA,2,Los Angeles,Downtown
+9,1,CA,2,Los Angeles,Los Feliz
+10,1,CA,2,Los Angeles,Koreatown
+11,1,MI,3,Detroit,Downtown
+12,1,MI,3,Detroit,Greektown
+13,1,MI,3,Detroit,Corktown
+14,1,MI,3,Detroit,Mexicantown
+15,2,MC,4,Memnonia,Arcadia Planitia
+'''.lstrip().replace('\n', '\r\n')
 
 def test_table_csv(app_client):
     response = app_client.get('/test_tables/simple_primary_key.csv')
@@ -19,6 +37,13 @@ def test_table_csv(app_client):
     assert EXPECTED_TABLE_CSV == response.text
 
 
+def test_table_csv_with_labels(app_client):
+    response = app_client.get('/test_tables/facetable.csv?_labels=1')
+    assert response.status == 200
+    assert 'text/plain; charset=utf-8' == response.headers['Content-Type']
+    assert EXPECTED_TABLE_WITH_LABELS_CSV == response.text
+
+
 def test_custom_sql_csv(app_client):
     response = app_client.get(
         '/test_tables.csv?sql=select+content+from+simple_primary_key+limit+2'

tests/test_html.py

@@ -388,6 +388,20 @@ 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_disable_foreign_key_links_with_labels(app_client):
+    response = app_client.get('/test_tables/foreign_key_references?_labels=off')
+    assert response.status == 200
+    table = Soup(response.body, 'html.parser').find('table')
+    expected = [
+        [
+            '<td class="col-pk"><a href="/test_tables/foreign_key_references/1">1</a></td>',
+            '<td class="col-foreign_key_with_label">1</td>',
+            '<td class="col-foreign_key_with_no_label">1</td>'
+        ]
+    ]
+    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')
     assert response.status == 200