Ruby-on-rails 如何从数组中删除活动记录对象
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how to remove active record object from array
提问by sangeethkumar
I have set of active record object in array.
我在数组中有一组活动记录对象。
I just want to delete on object from array not in database
我只想从不在数据库中的数组中删除对象
a = Model.limit(2)
b = Model.first
a.delete(b)
returning nil value
返回零值
Its not deleting
它没有删除
is there anyway?
有吗？
回答by Martin M
a.to_a - [b]
Background: a.to_aconvertrs the relation into an array in in memory.[b]is an array whith just the element, you want to delete (in memory).a.to_a - [b]does an array substraction.
背景：a.to_a将关系转换为内存中的数组。[b]是一个只包含要删除的元素的数组（在内存中）。a.to_a - [b]做一个数组减法。
(In Rails 3.2 .to_a was applied automatically to a relation when it was accessed. I agree with gregates: It's better to convert the relation to an array explicitly)
（在 Rails 3.2 中，.to_a 在访问时自动应用于关系。我同意gregates：最好将关系显式转换为数组）
回答by gregates
There's potentially some confusion here because in ActiveRecord, Model.limit(2)does not return an array.
有可能一些混乱，因为这里在ActiveRecord，Model.limit(2)不返回数组。
Model.limit(2).class #=> ActiveRecordRelation
So when you call a.delete(b), you may not be calling Array#delete.
所以当你打电话时a.delete(b)，你可能不会打电话Array#delete。
Try this instead:
试试这个：
a = Model.limit(2).to_a # Executes the query and returns an array
b = Model.first
a.delete(b)
回答by itz2k13
This is what you need:
这是你需要的：
objects_in_db = Model.all
objects_in_array = Model.first(2)
objects_in_array.delete_if { |obj| !objects_in_db.include?(obj)}
In your case, Model.limit(2)may not return the first two object and so the array amay not contain band hence, it returns nil.
在您的情况下，Model.limit(2)可能不会返回前两个对象，因此数组a可能不包含b，因此，它返回nil.
