Today I Learned

A Hashrocket project

Named bindings in Ecto (vs positional bindings)

Positional bindings in Ecto are meant to confuse when buildings large queries across several different functions.

query = Thing
|> join(:inner, [t], x in X, on: t.x_id = x.id)
|> join(:inner, [_, x], y in Y, on: x.y_id = y.id)

Using that query in another function might look like this:

query
|> where([_, x, _], x.type == "Articulated")

But what if the positions change? How am I supposed to know which positions are which when Iโ€™m adding to this query out of context?

Named bindings help tremendously here (note the :as option):

query = Thing
|> join(:inner, [t], x in X, as: :x, on: t.x_id = x.id)
|> join(:inner, [_, x], y in Y, as: :y, on: x.y_id = y.id)

Now I can refer to these things without knowing the position. If the position changes itโ€™s all good the additive where statement does not have to change:

query
|> where([y: y, x: x], x.type == "Articulated", y.feel == "Good")
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