Add a way to enforce an empty result set for a database condition query

+++ b/core/lib/Drupal/Core/Database/Query/QueryConditionTrait.php
@@ -63,6 +63,14 @@ public function notExists(SelectInterface $select) {
+    $this->condition->where('1 = 0');

I think this can be $this->condition->alwaysFalse()?

This looks good to me. We do need a change record for this.

+++ b/core/tests/Drupal/KernelTests/Core/Database/SelectTest.php
@@ -252,6 +252,27 @@ public function testIsNotNullCondition() {
+    $names = db_select('test', 'test')
...
+    $names = db_select('test', 'test')

db_select() is deprecated. Let's not add new usages - especially when $this->connection is available. Don't update the rest of the test though - thats not in scope.

+1 to the change record.

Should we not add a deprecation notice with the condition method that ->condition('1 <> 1') will not longer work after the release of Drupal 9.0.

One thing to note is that ->condition('1 <> 1') only works by complete and utter accident!

Checkout the output for

$query = db_select('node');
$query->condition('1 <> 1');
var_dump((string) $query);

it's

string(64) "SELECT
FROM
{node} node
WHERE 11 = :db_condition_placeholder_0"]

And the value for :db_condition_placeholder_0 is an empty string. So by complete fluke it works.

I think we should consider deprecating the ability to pass a string for $field and NULL for $value and $operator is equal to = (its default value) in \Drupal\Core\Database\Query\ConditionInterface::condition(). The only time a NULL for $value makes sense is if $field is a \Drupal\Core\Database\Query\ConditionInterface or $operation is a unary operator.

Here's probably the best way to deprecate this... let's see what falls out the trees.

The change record looks good. The new method is documented correctly and there is test coverage of nearly everything. The only thing missing coverage afaics is:

+++ b/core/lib/Drupal/Core/Database/Query/SelectExtender.php
@@ -474,6 +474,14 @@ public function notExists(SelectInterface $select) {
+  public function alwaysFalse() {
+    $this->query->alwaysFalse();
+    return $this;
+  }

There is no test coverage of this. We should add some by repeating the test added and doing ->extend('Drupal\Core\Database\Query\SelectExtender')

Thanks @amateescu - as per #18 - now everything is addressed.

This is a good idea. +1 for RTBC

I initially expected the method to be falsify(), so that it's a verb and not an adjective, but maybe that makes the method less obvious.

Committed 8f1228f and pushed to 8.7.x. Thanks!