Nobylcher
How to compare a fragment with a query reference variable in ecto?
So, let’s say I have a model Car, and a model Person, with a structures:
%Car{id: "123"}
%Person{
options: "{"car_id":"123"}"
}
options being a text field on the underlying DB.
To fetch that from the database I can use a fragment like:
"JSON_EXTRACT(?, \"$.car_id\")"
It works when using the order_by statement for example, however, when fetching all Persons and joining all the related Cars based on that fragment, it doesn’t…
I tried this, and put that return value on the select statement to try to debug:
from p in Person,
join: c in Car, on: c.id == fragment("JSON_EXTRACT(?, \"$.car_id\")" p.options),
select: {c.id == fragment("JSON_EXTRACT(?, \"$.car_id\")" p.options), fragment("JSON_EXTRACT(?, \"$.car_id\")" p.options), c.id}
which basically returns [{false, "123", "123"}] (false on every comparison)
I would be grateful if somebody had a hint for this.
Marked As Solved
Nobylcher
using UNHEX(JSON_UNQUOTE(JSON_EXTRACT(...))) solved the problem.
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idi527

Are you using MySQL? I couldn’t find JSON_EXTRACT function in Postgres …
Judging by https://stackoverflow.com/questions/39818296/using-mysql-json-field-to-join-on-a-table, you might need to use JSON_UNQUOTE in the join expression like
from p in Person,
join: c in Car, on: c.id == fragment("JSON_UNQUOTE(JSON_EXTRACT(?, \"$.car_id\"))" p.options),
select: {c.id == fragment("JSON_UNQUOTE(JSON_EXTRACT(?, \"$.car_id\"))" p.options), fragment("JSON_EXTRACT(?, \"$.car_id\")" p.options), c.id}







