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Result Reading

With the default preRead=true, find / findOne expand document fields for entity mapping. Without a projection, _ID and _JSON document columns are also available.

Read Projected Fields​

A projection returns only the projected fields, without synthetic _ID or _JSON columns. Inclusion projections preserve the declared column order. MongoDB includes _id by default, so exclude it explicitly when reading a single business field:

String name = jdbc.queryForString(
        "test.user_info.find({uid: ?}, {_id: 0, name: 1})",
        new Object[] { "1001" });

Read a Field by Name​

Without a projection, read business fields by column name:

List<String> names = jdbc.queryForList(
        "test.user_info.find({uid: ?})",
        new Object[] { "1001" },
        (rs, rowNum) -> rs.getString("name"));

With preRead=false, read the original document instead of expecting expanded columns:

List<String> documents = jdbc.queryForList(
        "test.user_info.find({}).limit(10)",
        (rs, rowNum) -> rs.getString("_JSON"));

Without an output projection, read aggregate documents from _JSON. To map group results or computed fields to properties, add $project at the end of the pipeline; the default preRead=true exposes those fields as result columns. _ID exposes ObjectId values only; read numeric or string _id from the document field.

Limit the Returned Data​

Specify limit on find or $limit in aggregate. Disabling preRead does not make ResultSet.next() fetch one server page at a time.

For JSON-to-object mapping, see JSON Field Mapping.