search backwards in an one-to-many association

rubyonrails-talk
1

I am going to implement a small and simple search feature in my project. But got a question about the scenario I have right now. So hope to get some tips from here.

First of all, this is a rails app.

There are two models, A and C.

A has_many C.

That’s to say, it might have some situation like this:

A1 related to C1, C2, C3, C4 A2 related to C2, C3, C4, C5 A3 related to C2, C3, C4, C8 A4 related to C3, C4, C8, C9 A5 related to C4, C8, C9, C20

Use C2, C3, C4 as keyword, I can get A1, A2, A3

Use C4, C8, C9 as keyword, I can get A4, A5

I consider that this can be done by using something straightforward like A.Cs.includes?(C2,C3,C4).

But that requires an iteration of A. And I concern that it would have some performance issue.

Any advice or idea about this requirement ?

Thank you all, guys.

2

I am going to implement a small and simple search feature in my project. But got a question about the scenario I have right now. So hope to get some tips from here.

First of all, this is a rails app.

There are two models, A and C.

A has_many C.

That's to say, it might have some situation like this:

A1 related to C1, C2, C3, C4 A2 related to C2, C3, C4, C5 A3 related to C2, C3, C4, C8 A4 related to C3, C4, C8, C9 A5 related to C4, C8, C9, C20

For that you need A has_and_belongs_many C, or (my preferred solution) introduce a join model/table and use has_many through. You can't use has_many as that would require C belongs_to A which is not correct.

Use C2, C3, C4 as keyword, I can get A1, A2, A3 Use C4, C8, C9 as keyword, I can get A4, A5

I consider that this can be done by using something straightforward like A.Cs.includes?(C2,C3,C4).

But that requires an iteration of A. And I concern that it would have some performance issue.

Any advice or idea about this requirement ?

I don't understand exactly what your requirement is. in particular what do you mean by "use C2, C3, C4 as keyword", when each of the Cs is a record in the db. If you are trying to get all the As related to records C2, C3 and C4 then that is something like (c2.as + c3.as +c4.as).uniq though that may not be the most efficient way.

Colin

3

My mistake not making it clear enough.

Actually they have some attributes.

Let’s say,

A has a simple attribute called A.name and C also has a attribute C.name.

Then A has_many C, which means C.a_id exists.

In my case, my requirement is that if users enter C2.name、 C3.name and C4.name, I should show them A1.name or whatever attributes A might have that needs to be displayed.

Anyway, thanks for your reply.

4

No, still not getting it. When you say user enters C2.name, C3.name and C4.name do you mean he actually enters the string "C2.name, C3.name and C4.name" or do you mean he enters actual names or what? Please give an example of actual records and their fields and values and exactly what the user might enter and what you want to show.

Colin

5

If you want to load matching As without instantiating the Cs, you could do something like:

A.where(id: C.where(code: params[:codes]).pluck(:a_id))

If you are going to instantiate all As and Cs found anyway, you could just use eager loading:

found_c = C.where(code: params[:codes]).includes(:a)

found_a = found_c.collect(&:a).uniq

Jim

6

A for person, C for organization, which means they both have names.

Like, a person called John Terry, and he is affiliated to three organizations called Chelsea FC, London Something, and UK Good Football Player. ( I made up the other two org.)

So now if users want to find out some people that belong to these three organizations simultaneously, enter “Chelsea FC, London Something, UK Good Football Player”, system will show John Terry and other people who might meat this criteria as well.

Hope this time I make myself clear.

Thank you for your time.

7

Thank you, I’ll check this out.

8

I don't understand the associations then. Does an organisation have a number of affiliated people? Does a person have many organisations to which he is affiliated? If so then you want has_and_belongs_to_many or has_many_through as I said earlier.

By the way, I would find it easier to follow the thread if you could not top post, but insert your comments at appropriate places in the previous post. Thanks.

Colin

9

A for person, C for organization, which means they both have names.

Like, a person called John Terry, and he is affiliated to three

organizations called Chelsea FC, London Something, and UK Good Football

Player. ( I made up the other two org.)

I don’t understand the associations then. Does an organisation have a

number of affiliated people? Does a person have many organisations to

which he is affiliated? If so then you want has_and_belongs_to_many

or has_many_through as I said earlier.

Yes, I guess I know how to do it now.

By the way, I would find it easier to follow the thread if you could

not top post, but insert your comments at appropriate places in the

previous post. Thanks.

You mean I should reply like this? Got it.

Thank you.

10

I missed the requirement that each A found should contain all desired C records. These queries will find As with any of the C records found.

Jim Crate

11

> A for person, C for organization, which means they both have names. > > Like, a person called John Terry, and he is affiliated to three > organizations called Chelsea FC, London Something, and UK Good Football > Player. ( I made up the other two org.)

I don't understand the associations then. Does an organisation have a number of affiliated people? Does a person have many organisations to which he is affiliated? If so then you want has_and_belongs_to_many or has_many_through as I said earlier.

Yes, I guess I know how to do it now.

Excellent.

By the way, I would find it easier to follow the thread if you could not top post, but insert your comments at appropriate places in the previous post. Thanks.

You mean I should reply like this? Got it.

Yes please, the list does not have a specific requirement but personally I find it much better as one does not have to search down looking for what is being replied to. For someone asking a question it is not so much of an issue as they know what they asked but for those asking who maybe have a dozen questions on the go in a number of mailing lists then the context of each question is not necessarily immediately remembered.

Thank you.

Glad to be of help

Colin