server/springboot: alter "list tickets" SQL query on the fly

One learning is that we cannot rely on the "method name to SQL query"
magic that JPA supports -- rewriting queries using QueryRewriter only
works for JPQL or "native" (=dialect of the database) queries.

lmgty:
JPQL (Java Persistence Query Language) is a query language used to perform
database operations on entities defined in JPA (Java Persistence API). It
is similar to SQL but operates on the entity objects instead of the
database tables.

Signed-off-by: Stephan Renatus <[email protected]>

server/springboot/src/main/java/com/styra/tickethub_springboot/dao/model/TicketRepository.java

@@ -1,12 +1,42 @@
 package com.styra.tickethub_springboot.dao.model;
 
+import com.styra.tickethub_springboot.App;
+import java.util.List;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.data.domain.Sort;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.jpa.repository.QueryRewriter;
+import org.springframework.data.repository.query.Param;
 import org.springframework.stereotype.Repository;
 
-import java.util.List;
-
 @Repository
-public interface TicketRepository extends JpaRepository<Ticket, Integer> {
-    List<Ticket> findByTenant(Tenant tenant);
+public interface TicketRepository
+    extends JpaRepository<Ticket, Integer>, QueryRewriter {
+    @Query(
+        value = "SELECT t.id, t.customer, t.description, t.last_updated, t.resolved, t.tenant FROM \"Tickets\" t LEFT JOIN \"Tenants\" t1 ON t1.id=t.tenant WHERE t1.name=:#{#tenant.name}",
+        nativeQuery = true,
+        queryRewriter = TicketRepository.class
+    )
+    List<Ticket> findByTenant(@Param("tenant") Tenant tenant);
+
     List<Ticket> findByTenantAndId(Tenant tenant, Integer id);
+
+    @Override
+    default String rewrite(String query, Sort sort) {
+        // Omitted:
+        // 1. get conditions from OPA, after feeding it query and user information
+        // 2. convert conditions to SQL WHERE clause
+        //
+        // SQL logging uncovered **a lot** of queries happening for "list tickets".
+        // I'd assume that they're done automatically by Spring Data JPA, to ensure
+        // relationships etc; but it also means they are under the radar of this rewriter.
+        // However, I'd envision that there's one rewriter that would be used with all
+        // the repositories, so maybe we would end up covering call queries after all.
+        String rewritten = query + " AND t.resolved = false"; // leading space is crucial
+        Logger logger = LoggerFactory.getLogger(App.class);
+        logger.info("rewritten: " + rewritten);
+        return rewritten;
+    }
 }

server/springboot/src/main/resources/application.properties

@@ -37,3 +37,9 @@ logging.level.com.styra.tickethub_springboot.dao.model=TRACE
 # production, you probably shouldn't do this.
 spring.security.user.name=demouser
 spring.security.user.password=letmein
+
+# dump all the SQL
+spring.jpa.show-sql=true
+spring.jpa.properties.hibernate.format_sql=true
+logging.level.org.hibernate.SQL=DEBUG
+logging.level.org.hibernate.type.descriptor.sql.BasicBinder=TRACE