How to create a query dynamically?

[vincent-herlemont]

Is there a way to create a query dynamically, meaning to construct different blocks of the query following certain logic?

A simple case: I may or may not want a filter to be applied to the query, and I want to avoid writing two separate queries for this.

Here's what I naively did; however, it doesn't compile because I don't know what to put in table.filter(??) when there is no condition, and I have to put something to respect the typing of the if branches:

    let table = nodes::table;

    let query = if let Some(filter) = filter {
        table.filter(nodes::name.eq("Node2"))
    } else {
        table.filter(??)
    };

    query.load::<Node>(conn);

Undoubtedly my method is not correct, do you have any suggestions?

[weiznich]

See the documentation of QueryDsl::into_boxed for a solution.

[vincent-herlemont]

Thanks works perfectly!

Result

    let mut query = nodes::table.into_boxed();

    if let Some(_) = filter {
        query = query.filter(nodes::name.eq("Node2"))
    };

    query.load::<Node>(conn);