Add function to check LastInsertId-ability

- Previously we used a lot of template magic to see if we could
  use LastInsertId. But there's a much simpler check that's worth doing,
  do this at the table level and then let it fall through.

bdb/table.go

@@ -40,3 +40,27 @@ func (t Table) GetColumn(name string) (col Column) {
 
 	panic(fmt.Sprintf("could not find column name: %s", name))
 }
+
+// CanLastInsertID checks the following:
+// 1. Is there only one primary key?
+// 2. Does the primary key column have a default value?
+// 3. Is the primary key column type one of uintX/intX?
+// If the above is all true, this table can use LastInsertId
+func (t Table) CanLastInsertID() bool {
+	if t.PKey == nil || len(t.PKey.Columns) != 1 {
+		return false
+	}
+
+	col := t.GetColumn(t.PKey.Columns[0])
+	if len(col.Default) == 0 {
+		return false
+	}
+
+	switch col.Type {
+	case "int", "int8", "int16", "int32", "int64", "uint", "uint8", "uint16", "uint32", "uint64":
+	default:
+		return false
+	}
+
+	return true
+}

bdb/table_test.go

@@ -65,3 +65,56 @@ func TestGetColumnMissing(t *testing.T) {
 
 	table.GetColumn("missing")
 }
+
+func TestCanLastInsertID(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		Can   bool
+		PKeys []Column
+	}{
+		{true, []Column{
+			{Name: "id", Type: "int64", Default: "a"},
+		}},
+		{true, []Column{
+			{Name: "id", Type: "uint64", Default: "a"},
+		}},
+		{true, []Column{
+			{Name: "id", Type: "int", Default: "a"},
+		}},
+		{true, []Column{
+			{Name: "id", Type: "uint", Default: "a"},
+		}},
+		{true, []Column{
+			{Name: "id", Type: "uint", Default: "a"},
+		}},
+		{false, []Column{
+			{Name: "id", Type: "uint", Default: "a"},
+			{Name: "id2", Type: "uint", Default: "a"},
+		}},
+		{false, []Column{
+			{Name: "id", Type: "string", Default: "a"},
+		}},
+		{false, []Column{
+			{Name: "id", Type: "int", Default: ""},
+		}},
+		{false, nil},
+	}
+
+	for i, test := range tests {
+		table := Table{
+			Columns: test.PKeys,
+			PKey:    &PrimaryKey{},
+		}
+
+		var pkeyNames []string
+		for _, pk := range test.PKeys {
+			pkeyNames = append(pkeyNames, pk.Name)
+		}
+		table.PKey.Columns = pkeyNames
+
+		if got := table.CanLastInsertID(); got != test.Can {
+			t.Errorf("%d) wrong: %t", i, got)
+		}
+	}
+}