ar.rs

trait Queryable {
    fn pluralized_table_name(&self) -> String;

    fn predicates(&self) -> &Vec<String>;

    fn has_limit(&self) -> bool {
        return self.limit_value() >= 0;
    }

    fn limit_value(&self) -> i64;

    fn to_sql(&self) -> String {
        let mut query_string = "SELECT * FROM ".to_string();
        query_string = query_string + &self.pluralized_table_name();

        let mut and_predicate = false;
        for predicate in self.predicates() {
            if and_predicate {
                query_string = query_string + " AND"
            }

            query_string = query_string + " " + &predicate.to_string();

            and_predicate = true;
        }

        if self.has_limit() {
            query_string = query_string + " LIMIT " + &self.limit_value().to_string();
        }

        query_string = query_string + ";";

        return query_string;
    }
}

#[derive(Clone)]
struct Query {
    table: &'static str,
    predicates: Vec<String>,
    limit: i64
}

impl Query {
    pub fn new(table: &'static str) -> Query {
        return Query{table: table, predicates: Vec::new(), limit: -1};
    }

    pub fn from(table: &'static str) -> Query {
        return Query::new(table);
    }

    pub fn limit(&mut self, n: i64) -> Query {
        self.limit = n;
        return self.clone()
    }

    pub fn where_eq(&mut self, attribute: &'static str, value: &'static str) -> Query {
        let predicate = "WHERE '".to_string() + &attribute.to_string() + "' = '" + &value.to_string() + "'";
        self.predicates.push(predicate);
        return self.clone();
    }
}

impl Queryable for Query {
    fn pluralized_table_name(&self) -> String {
        return self.table.to_string();
    }

    fn predicates(&self) -> &Vec<String> {
        return &self.predicates;
    }

    fn limit_value(&self) -> i64 {
        return self.limit;
    }
}

fn main() {
    let query = Query::from("transactions").where_eq("name", "roger").where_eq("gender", "m").limit(10);

    println!("{}", query.to_sql());
}

//=> SELECT * FROM transactions WHERE 'name' = 'roger' AND WHERE 'gender' = 'm' LIMIT 10;