Criteria, Query, and Update DSL

Criteria remains a Spring Data object

Extensions such as eq, gt, inValues, regex, and andWith do not create another query engine. They are Kotlin infix aliases for methods on Spring Data Criteria.

val criteria =
    ("age".criteria() gte 20) andWith
        ("city".criteria() inValues listOf("Seoul", "Busan"))

criteriaOf(c1, c2) combines conditions with $and. Field-existence, null, array-size, element-match, and regex helpers produce the corresponding Spring Data BSON structures.

Build a Query

val query = queryOf(
    "status".criteria() ne "deleted",
    "age".criteria() gte 20,
).sortDescBy("createdAt")
 .paginate(page = 0, size = 50)

queryOf() creates an empty Query for no arguments, a single-criteria query for one, and an $and query for several. sortBy, sortAscBy, sortDescBy, limitTo, skipTo, and paginate mutate and return the same Query.

paginate(page, size) is only skip(page * size).limit(size). It does not validate arguments. Reject negative pages and non-positive sizes at the controller boundary, and limit large offsets and multiplication ranges.

Build an Update

val update = ("name" setTo "Alice")
    .andSet("city", "Seoul")
    .andInc("loginCount", 1)
    .andPush("history", "signed-in")

updateOf("name" to "Alice", "age" to 31) turns every pair into $set. setTo, incBy, unsetField, pushValue, and pullValue start one operation; andSet, andInc, andUnset, and andPush add more operations.

String field boundaries

The DSL accepts document properties as strings. The compiler cannot find typos or renames, so centralize frequently used names or derive them from mapping metadata. Never pass an HTTP parameter directly as a field name or regex; apply an allowlist and input limits.

Unit-testing the DSL

Criteria, Query, and Update tests do not start MongoDB. They compare criteriaObject, queryObject, sortObject, and updateObject with objects produced by the standard Spring Data API. This is the fastest regression test when extending the DSL.

Source and tests

• CriteriaExtensions.kt
• QueryExtensions.kt
• UpdateExtensions.kt
• CriteriaExtensionsTest.kt
• QueryExtensionsTest.kt
• UpdateExtensionsTest.kt

Next chapter

Move beyond ordinary finds in Aggregation, collections, and streaming.