Syntax error in query

Questions / Help
1

I have this query I wrote for testing the library.

   expect = from j in Test.JoinModel, join: e in assoc(j, :example),
   preload: [example:  from w in Test.WhereModel,  limit: ^3 , offset: ^0]

It throws this error while compiling:

         unexpected comma. Parentheses are required to solve ambiguity inside containers

Any help will be appreciated.
Thanks

2

You need to add parentheses to resolve ambiguity. I tend to add them around the whole from, like so:

   expect = from(
      j in Test.JoinModel,
      join: e in assoc(j, :example),
      preload: [example:  from(w in Test.WhereModel,  limit: ^3 , offset: ^0)]
   )

Strictly speaking only the parentheses around the inner from are required, because without them Elixir doesn’t know if you are adding more options for the from or the preload.

1 Like
3

Thanks for you reply .It still throws an error. This time this one:

    from(w in Test.WhereModel, limit: 3, offset: 0)` is not a valid preload expression. preload expects an atom,a list of atoms or a keyword list with more preloads as values. Use ^ on the outermost preload to interpolate a value
4

I’m not that well versed with assocs and preloads so hope someone else can respond about that.

5

Hi, if you are playing with ecto, try better schema names, it truly helps.

You don’t need ^ for numbers, only for named variables like ^limit or ^offset.

If you want to preload an association with a join you should:

from(user in User,
     join: posts in assoc(user, :posts),
     preload: [posts: posts],
     limit: 3,
     offset: 0)

And if you want to do with a query (this performs two queries in the database):

post_query = from(post in Post, limit: 3, offset: 0)
from(user in User,
     preload: [posts: ^post_query],
     limit: 3,
     offset: 0)

However, take a look at the ecto documentation:

Note: keep in mind operations like limit and offset in the preload query will affect the whole result set and not each association. For example, the query below:

comments_query = from c in Comment, order_by: c.popularity, limit: 5
Repo.all from p in Post, preload: [comments: ^comments_query]

won’t bring the top of comments per post. Rather, it will only bring the 5 top comments across all posts.

1 Like
6

Thanks for your feedback.

1 Like