You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: read.rs
    path of file: ./repos/prisma-engines/query-engine/core/src/query_ast
    
    the code of the file until where you have to start completion: //! Prisma read query AST
use super::FilteredQuery;
use crate::ToGraphvi
    
    fn returns(&self) -> Option<&FieldSelection> {
        match self {
            ReadQuery::RecordQuery(x) => Some(&x.selected_fields),
            ReadQuery::ManyRecordsQuery(x) => Some(&x.selected_fields),
            ReadQuery::RelatedRecordsQuery(x) => Some(&x.selected_fields),
            ReadQuery::AggregateRecordsQuery(_x) => None,
        }
    }