Query: Always use INNER join to establish the outer query link - #173
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This is required to establish type symmetry as the base's methods also accept `NULL` to be able to direcly pass a getters return value to the appropriate setter.
There is now `Relation::bindTo(Model, string, Resolver)` in order to pass control to relations how they're prepared. Since the introduction of `BelongsToMany`, it is established that a relation may resolve to multiple hops and thus needs to perform steps n-times rather than a single time. It's this reason because registering the alias and resolving the filter is now a responsibility of a relation rather than the resolver. Relations know it better how to and the override of `bindTo` in `BelongsToMany` proves it as it turned out that it is necessary to allow referencing the junction table in either the filter or the through filter in order to be able to better reverse relations. Qualification must be done by a relation in turn as well, as otherwise there's a mis-match with what's allowed to reference and what can be qualified. My initial attempt was to teach `Relation::resolve()` this, but without passing it the resolver and changing the return value this doesn't make sense. Sadly, this is out of the question as this is a breaking change. Say hello to `Relation::setFilterSubjects()` due to this.
Changes the way relations can be reversed drastically as it is now possible to influence the relation to use during reversal with `::setReverseName(string)` which allows Icinga DB Web to drop the error-prone `to.from` and `from.to` relations. An additional change is that it is now not mandatory anymore to define relations that are solely being required because of sub-queries. Missing relations on the reversed path are automatically registered. For this, each relation type now has its specific counterpart which is possible to override with `::setReverseClass(class-string)`. The default however, is to use the same type which is the case for `BelongsToOne` and `BelongsToMany`. For `BelongsTo` a sane override has been chosen that is based on how it's used at the moment in our products, as `HasOne` and `HasMany` may both be appropriate. But the latter clearly is used more often.
Since `::reverse()` uses the source's table alias by default as reverse name, a deprecation notice is triggered if the original forward path uses a different name, indicating that it is necessary to use this name as explicit reverse name. fixes #170
A subquery always needs to establish a link, be it part of a WHERE or solely used to eager load (using `Query::derive`) a relation. Using an INNER join allows the database to apply optimizations it wouldn't be able to otherwise.
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A subquery always needs to establish a link, be it part of a WHERE or solely used to eager load (using
Query::derive) a relation. Using an INNER join allows the database to apply optimizations it wouldn't be able to otherwise.Since this affects
Query::derive(), any eager loaded relation will now return no result. But this should be usually not a problem, as a caller that iterates or callsfirst()without handling the never entered loop ornull-return is already bugged, IMHO. I've checked this with Icinga DB Web and found exactly two cases: Icinga/icingadb-web#1408Still attempting to prove this is actually of advantage, though…