4.x: Fix DbClient JSON mapping

- DbColumn.get() overrides Value.get() using as() instead of as().get() thus it returns an instance of Value instead of the raw value.
- Add a unit test in dbclient/jsonp

Fixes helidon-io#7842

Author: romain-grecourt

dbclient/dbclient/src/main/java/io/helidon/dbclient/DbColumn.java

@@ -60,7 +60,7 @@ public interface DbColumn extends Value<Object> {
      */
     @Override
     default Object get() {
-        return as(javaType());
+        return as(javaType()).get();
     }
 
     /**

dbclient/jsonp/pom.xml

@@ -43,6 +43,16 @@
             <artifactId>helidon-common-features-api</artifactId>
             <optional>true</optional>
         </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-all</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>

dbclient/jsonp/src/test/java/io/helidon/dbclient/jsonp/JsonProcessingMapperTest.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2023 Oracle and/or its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.helidon.dbclient.jsonp;
+
+import io.helidon.common.mapper.MapperManager;
+import io.helidon.dbclient.DbColumn;
+import io.helidon.dbclient.DbColumnBase;
+import io.helidon.dbclient.DbMapperManager;
+import io.helidon.dbclient.DbRow;
+import io.helidon.dbclient.DbRowBase;
+
+import jakarta.json.JsonObject;
+import org.junit.jupiter.api.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+
+/**
+ * Tests {@link io.helidon.dbclient.jsonp.JsonProcessingMapper}.
+ */
+class JsonProcessingMapperTest {
+
+    private static final DbMapperManager DB_MAPPER_MANAGER = DbMapperManager.builder()
+            .addMapperProvider(new JsonProcessingMapperProvider())
+            .build();
+
+    @Test
+    void testRowAsJsonObject() {
+        DbRow row = row(column("foo", "bar"), column("bob", "alice"));
+        JsonObject jsonObject = row.as(JsonObject.class);
+        assertThat(jsonObject.getString("foo"), is("bar"));
+    }
+
+    private static DbRow row(DbColumnBase... columns) {
+        return new DbRowBase(columns, DB_MAPPER_MANAGER) {
+            @Override
+            public DbColumn column(String name) {
+                return super.column(name);
+            }
+        };
+    }
+
+    private static DbColumnBase column(String name, Object value) {
+        return new DbColumnBase(value, MapperManager.create()) {
+
+            @Override
+            public Class<?> javaType() {
+                return value.getClass();
+            }
+
+            @Override
+            public String dbType() {
+                return "test";
+            }
+
+            @Override
+            public String name() {
+                return name;
+            }
+        };
+    }
+}