Add Expression functionality

[peteraba]

Feature to enable setting values via SQL expressions and not just simple values.

values in expressions

Strictly speaking Expression doesn't have to handle values, but it's probably nicer to set up queries with it.

With Expressions handling values:

$expr = new Expression('(val + ?) % ?', ['1', PDO::PARAM_INT], [2, PDO::PARAM_INT]);
$query = new UpdateQuery('users', 'u', ['name' => 'david']);
$query->addColumnValues(['email' => 'bar@foo.com', 'is_val_even' => $expr])
    ->where('u.id = ?', 'emails.userid = u.id', 'emails.email = ?')
    ->orWhere('u.name = ?')
    ->andWhere('subscriptions.userid = u.id', "subscriptions.type = 'customer'")
    ->addUnnamedPlaceholderValues([[18175, PDO::PARAM_INT], 'foo@bar.com', 'dave']);

Without this features it becomes:

$expr = new Expression('(val + ?) % ?');
$query = new UpdateQuery('users', 'u', ['name' => 'david']);
$query->addColumnValues(['email' => 'bar@foo.com', 'is_val_even' => $expr])
    ->where('u.id = ?', 'emails.userid = u.id', 'emails.email = ?')
    ->orWhere('u.name = ?')
    ->andWhere('subscriptions.userid = u.id', "subscriptions.type = 'customer'")
    ->addUnnamedPlaceholderValues([[1, \PDO::PARAM_INT], [2, PDO::PARAM_INT], [18175, PDO::PARAM_INT], 'foo@bar.com', 'dave']);

If you feel this feature is not needed, just let me know and I'll remove it.

[davidbyoung]

Nice work. A few questions:

• Could/should expressions ever allow sub-expressions?
• Could/should DELETE queries support expressions?

[peteraba]

Thanks, glad you like it.

Regarding the questions:

1. Well, originally class Expression was called Upsert because I was planning to have another expression class called Column to support SELECT queries. It was not really obvious from the documentation that it was already supported, but then I saw that SelectQuery::__construct already takes expressions. Anyway I'll move Expression into QueryBuilders.
2. Since WHERE and HAVING clauses already support expressions, I don't really see how they should be affected.