Iterating over the rows with mapping example

[waynenilsen]

Would it be possible to add an example to the readme? I have a similar example to the one from the readme but cannot seem to figure out how to do the same thing but get the results into a vector using iterator mapping.

So, this works

        let conn = get_connection();
        let stmt = conn.prepare("SELECT id, firstname, lastname FROM person").unwrap();
        for row in stmt.query(&[]).unwrap() {
            let person = Person {
                firstname: row.get(1),
                lastname: row.get(2),
            };
            println!("Found person {}", person.firstname);
        }

But I have to specify the type of row during the mapping which seems like it should be Option<Row<'a> it seems.

        get_connection()
            .prepare("SELECT id, firstname, lastname FROM person").unwrap()
            .query(&[]).unwrap()
            .iter().map( | row | {
                Person {
                    firstname: row.get(1),
                    lastname: row.get(2),
                }
        }).collect().to_json()

I feel like I'm close, any suggestions? The code above does not work but it "feels" pretty close.

[sfackler]

What specific error are you seeing? It looks like the compiler would be complaining about not knowing what the return type of collect is there. All it knows there is that it's something that has a to_json method, but that could include all kinds of things. Changing collect() to collect::<Vec<_>>() might help.

[waynenilsen]

This worked, thank you for your tip regarding the collect type hint, it turns out that is what the compiler was complaining about (at first).

        let conn = get_connection();
        let stmt = conn.prepare("SELECT id, firstname, lastname FROM person").unwrap();
        stmt
            .query(&[]).unwrap()
            .iter().map( | row | {
                Person {
                    firstname: row.get(1),
                    lastname: row.get(2),
                }
        }).collect::<Vec<_>>().to_json()

I wish I could have done

        get_connection()
            .prepare("SELECT id, firstname, lastname FROM person").unwrap()
            .query(&[]).unwrap()
            .iter().map( | row | {
                Person {
                    firstname: row.get(1),
                    lastname: row.get(2),
                }
        }).collect::<Vec<_>>().to_json()

but I get error: borrowed value does not live long enough. I guess that is just the borrow checker working the &self cases like fn xyz(&self, ...)

[sfackler]

Yeah, there's a bit of a balancing act for cases like that to both make rules in the compiler covering how long the value lasts that are both comprehensible and work in as many cases as possible.