fetch rows as serde_json::Value

query_as_json.rs

use oracle::{sql_type::OracleType, sql_type::ToSql, Connection, ResultSet, Row};
use std::str::FromStr;

// Usage:
//
//  // conn is oracle::Connection.
//  for json_result in query_as_json(&conn, sql, &[])? {
//      // json_result is std::result::Result<serde_json::Value, oracle::Error>.
//      let json = json_result?;
//      println!("{}", json);
//  }

pub fn query_as_json<'a>(
    conn: &'a Connection,
    sql: &str,
    params: &[&dyn ToSql],
) -> oracle::Result<JsonRowIterator<'a>> {
    Ok(JsonRowIterator::new(conn.query(sql, params)?))
}

pub struct JsonRowIterator<'a> {
    result_set: ResultSet<'a, Row>,
}

impl<'a> JsonRowIterator<'a> {
    fn new(rs: ResultSet<'a, Row>) -> JsonRowIterator<'a> {
        JsonRowIterator { result_set: rs }
    }

    fn json_from_row(&self, row: Row) -> oracle::Result<serde_json::Value> {
        let mut map = serde_json::Map::new();
        for (pos, colinfo) in self.result_set.column_info().iter().enumerate() {
            let value = match colinfo.oracle_type() {
                OracleType::BinaryFloat
                | OracleType::BinaryDouble
                | OracleType::Number(_, _)
                | OracleType::Float(_) => row.get::<usize, Option<String>>(pos)?.map(|val| {
                    match serde_json::Number::from_str(&val) {
                        Ok(num) => serde_json::Value::Number(num),
                        Err(_) => serde_json::Value::String(val),
                    }
                }),
                _ => row
                    .get::<usize, Option<String>>(pos)?
                    .map(serde_json::Value::String),
            };
            map.insert(
                colinfo.name().into(),
                value.unwrap_or(serde_json::Value::Null),
            );
        }
        Ok(serde_json::Value::Object(map))
    }
}

impl<'a> Iterator for JsonRowIterator<'a> {
    type Item = oracle::Result<serde_json::Value>;

    fn next(&mut self) -> Option<Self::Item> {
        let row_result = self.result_set.next()?;
        Some(row_result.and_then(|row| self.json_from_row(row)))
    }
}