Add failing test case for preload_associations_lazily for association defined with scope

[PikachuEXE]

Similar to #40
This is a bug I have no idea how to solve

[coveralls]

Pull Request Test Coverage Report for Build 303

• 11 of 11 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 95.908%

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Totals
Change from base Build 298:	0.05%
Covered Lines:	750
Relevant Lines:	782

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 300

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.9%) to 99.731%

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Totals
Change from base Build 298:	3.9%
Covered Lines:	741
Relevant Lines:	743

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💛 - Coveralls

[PikachuEXE]

@DmitryTsepelev
Help~
This is more annoying and cannot be workaround

[DmitryTsepelev]

Looks like the problem is in the way how #size method works on associations: when association is loaded—it calls #length, otherwise—initiates COUNT(*) DB call. Due to the gem implementation, association is loaded lazily when at least one element of a context is loaded. However, in the spec #size is called before association is loaded, so DB call is initiated (which is a useful behaviour—it can save developer from loading thousands of records to just count them in memory). I've changed a spec to use map (as usual) and added an extra spec, where #size is called after #map—both pass locally. What do you think?

[DmitryTsepelev]

BTW replacing #size with #length makes a trick too: when length is called for a first time, Rails goes to the DB, and preloading context loads all other records belonging to it, so the second #length call does not initiate a DB request

[PikachuEXE]

I see
Maybe another update for README?

[DmitryTsepelev]

Agreed, I'll do my best to do it today, thanks for the heads up! ✊

[PikachuEXE]

No need to rush
But I the build seems failing due to some system db query
No idea how to fix

[DmitryTsepelev]

Added the readme section and created an issue about extra DB calls