Training fetch code

for training_id in training_iter {
    let training_id = training_id.map_err(|e| format!("Error pulling worker trainings: {}", e))?;

    // get training from library
    let training = match TRAINING_LIB.with_lock(|lib| lib.get(&training_id.to_string())) {
        // if training is already in library, return i
        Some(training) => training,
        // if training is not in library, pull from database and add to library
        None => {
            match TRAINING_LIB.with_lock(|lib| {
                // pull training from database
                let training = Training::pull_new(&training_id.to_string(), &conn).map_err(|e| format!("Error pulling worker trainings: {}", e));
                // add training to library
                Ok(match training {
                    Ok(training) => lib.add(&training_id.to_string(), training),
                    Err(e) => {
                        return Err(e);
                    }
                })
            }) {
                // if training was successfully added to library, return it
                Ok(opt) => match opt {
                    Some(training) => training,
                    // if training was not found in database, return an error
                    None => return Err(format!("Error pulling worker trainings: training with id {} not found", training_id).into()),
                },
                // if training could not be added to library, return an error
                Err(e) => {
                    return Err(format!("Error adding training to library: {}", e).into());
                }
            }
        }
    };

    worker_trainings.push(training);
}