Supported Platforms

Kuery Client delegates database access to Spring Data and the configured JDBC/R2DBC driver. It may work with other Spring-supported databases, but the combinations below are the ones exercised by this repository's automated tests.

Continuously tested databases

Database	JDBC driver	R2DBC driver	Test environment
MySQL	com.mysql:mysql-connector-j	io.asyncer:r2dbc-mysql	MySQL 8.0.37 Testcontainer
PostgreSQL	org.postgresql:postgresql	org.postgresql:r2dbc-postgresql	PostgreSQL 16 Testcontainer
H2	com.h2database:h2	io.r2dbc:r2dbc-h2	In-memory database

The suite runs the shared client behavior against both JDBC and R2DBC. Driver-dependent features—including parameter binding, arrays, generated values, and database error handling—also run against real MySQL and PostgreSQL containers.

What “tested” means

The table describes the project's automated test matrix, not an exclusive allow-list. A database supported by Spring Data may work, but behavior outside this matrix is not continuously verified by this project.

For compatible Java, Gradle, Kotlin, Spring Boot, and Spring Data versions, see Compatibility. The compiler plugin targets JVM and Android/JVM compilations; JavaScript, Native, and Wasm compilations are not supported.

Database-dependent behavior

Empty collections in IN clauses

Spring expands an empty collection to IN (). H2 accepts that syntax and returns no rows, while MySQL and PostgreSQL reject it as invalid SQL. Guard the empty case before building the query:

suspend fun findByIds(ids: List<Long>): List<User> {
    if (ids.isEmpty()) return emptyList()

    return kueryClient
        .sql { +"SELECT * FROM users WHERE user_id IN ($ids)" }
        .list()
}

The same rule applies to the blocking client without suspend.

SQL arrays

An object array such as Array<String> is bound as one driver array value; it is not expanded as an IN list. This is useful with PostgreSQL array columns and = ANY(...). MySQL has no equivalent native array type, so use a non-empty Collection for an IN clause instead.

ByteArray is bound as one binary value rather than a SQL array. For other primitive arrays, R2DBC boxes the elements into an object array before binding, while JDBC passes the primitive array to the driver unchanged; support therefore depends on the client and driver combination.

Generated values

Generated-key labels and JVM value types come from the driver. For example, the tested MySQL R2DBC driver returns the requested user_id key as a Long, while MySQL Connector/J reports GENERATED_KEY as a BigInteger even when "user_id" was requested.

When only one value is requested and its label is not important, use the single map value and convert it to the application type:

val generated = kueryClient
    .sql { +"INSERT INTO users (username) VALUES ($username)" }
    .generatedValues("user_id")

val userId = (generated.values.single() as Number).toLong()

generatedValues(...) expects exactly one generated-key row. It throws when no keys are produced or when a statement produces multiple key rows. The exact keys available are database- and driver-dependent.

SQL syntax dialects

The dialect selected by sqlSyntaxCheck controls compile-time parser validation only. It does not configure the runtime driver and is not a declaration that every feature of that database has been tested.