Builder API

Write Conflicts

Ignore and Update use MongoDB upserts, locating documents by the mapped primary-key field. Adding @Column(primary = true) does not create a unique index. Create one on that field if duplicates must be prevented.

See Data Writes for usage and affected counts.

Query

Ordinary builder queries generate find. Computed projections and aggregates use MongoDB expressions, not SQL functions. For example, grouped counts use $sum below, not COUNT(*).

Pagination

Ordinary queries use skip and limit, with a separate count query. Pagination iteration fetches successive pages; order by a unique field for stable paging. See Pagination for custom aggregation pipelines.

Where Builder

Do not treat null inside notIn as SQL's three-valued logic. To exclude both a specified age and null fields, remove nulls from the input collection and use:

lambda.query(UserInfo.class)
        .notIn(UserInfo::getAge, List.of(20))
        .isNotNull(UserInfo::getAge)
        .queryForList();

Group By

groupBy generates a $group pipeline stage. Supply MongoDB aggregate expressions through applySelect:

List<Map<String, Object>> rows = lambda.query(UserInfo.class)
        .applySelect("{cnt: {$sum: 1}}")
        .groupBy("age").orderBy("age")
        .queryForMapList();

The result contains age and cnt. See Query Operations for full pipelines and projections.

Order By

Ascending, descending, and multi-field ordering are supported. The MongoDB dialect does not yet support OrderNullsStrategy.FIRST or LAST. Default ordering follows MongoDB's null ordering and is not an explicit null-placement strategy.

For explicit placement, use an aggregation pipeline that adds a sort key and then applies $sort.