Implemented table.lookup(...), closes #44

* Add pk column if missing from insert
* Implemented table.lookup(...)

tests/test_create.py

@@ -734,3 +734,8 @@ def test_cannot_provide_both_filename_and_memory():
         AssertionError, match="Either specify a filename_or_conn or pass memory=True"
     ):
         Database("/tmp/foo.db", memory=True)
+
+
+def test_creates_id_column(fresh_db):
+    last_pk = fresh_db.table("cats", pk="id").insert({"name": "barry"}).last_pk
+    assert [{"name": "barry", "id": last_pk}] == list(fresh_db["cats"].rows)

tests/test_lookup.py

@@ -0,0 +1,68 @@
+from sqlite_utils.db import Index
+import pytest
+
+
+def test_lookup_new_table(fresh_db):
+    species = fresh_db["species"]
+    palm_id = species.lookup({"name": "Palm"})
+    oak_id = species.lookup({"name": "Oak"})
+    cherry_id = species.lookup({"name": "Cherry"})
+    assert palm_id == species.lookup({"name": "Palm"})
+    assert oak_id == species.lookup({"name": "Oak"})
+    assert cherry_id == species.lookup({"name": "Cherry"})
+    assert palm_id != oak_id != cherry_id
+    # Ensure the correct indexes were created
+    assert [
+        Index(
+            seq=0,
+            name="idx_species_name",
+            unique=1,
+            origin="c",
+            partial=0,
+            columns=["name"],
+        )
+    ] == species.indexes
+
+
+def test_lookup_new_table_compound_key(fresh_db):
+    species = fresh_db["species"]
+    palm_id = species.lookup({"name": "Palm", "type": "Tree"})
+    oak_id = species.lookup({"name": "Oak", "type": "Tree"})
+    assert palm_id == species.lookup({"name": "Palm", "type": "Tree"})
+    assert oak_id == species.lookup({"name": "Oak", "type": "Tree"})
+    assert [
+        Index(
+            seq=0,
+            name="idx_species_name_type",
+            unique=1,
+            origin="c",
+            partial=0,
+            columns=["name", "type"],
+        )
+    ] == species.indexes
+
+
+def test_lookup_adds_unique_constraint_to_existing_table(fresh_db):
+    species = fresh_db.table("species", pk="id")
+    palm_id = species.insert({"name": "Palm"}).last_pk
+    species.insert({"name": "Oak"})
+    assert [] == species.indexes
+    assert palm_id == species.lookup({"name": "Palm"})
+    assert [
+        Index(
+            seq=0,
+            name="idx_species_name",
+            unique=1,
+            origin="c",
+            partial=0,
+            columns=["name"],
+        )
+    ] == species.indexes
+
+
+def test_lookup_fails_if_constraint_cannot_be_added(fresh_db):
+    species = fresh_db.table("species", pk="id")
+    species.insert_all([{"id": 1, "name": "Palm"}, {"id": 2, "name": "Palm"}])
+    # This will fail because the name column is not unique
+    with pytest.raises(Exception, match="UNIQUE constraint failed"):
+        species.lookup({"name": "Palm"})