diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java b/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
index 9f23a72d7..47dc3103c 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
@@ -22,6 +22,7 @@ package org.navalplanner.business.common;
 
 import org.navalplanner.business.advance.daos.IAdvanceTypeDAO;
 import org.navalplanner.business.calendars.daos.IBaseCalendarDAO;
+import org.navalplanner.business.common.daos.IConfigurationDAO;
 import org.navalplanner.business.costcategories.daos.ITypeOfWorkHoursDAO;
 import org.navalplanner.business.labels.daos.ILabelDAO;
 import org.navalplanner.business.labels.daos.ILabelTypeDAO;
@@ -88,6 +89,9 @@ public class Registry {
     @Autowired
     private ILabelTypeDAO labelTypeDAO;
 
+    @Autowired
+    private IConfigurationDAO configurationDAO;
+
     private Registry() {
     }
 
@@ -143,4 +147,8 @@ public class Registry {
         return getInstance().labelTypeDAO;
     }
 
+    public static IConfigurationDAO getConfigurationDAO() {
+        return getInstance().configurationDAO;
+    }
+
 }
\ No newline at end of file
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/Order.java b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/Order.java
index 38528fabd..c59d126f6 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/Order.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/Order.java
@@ -63,7 +63,7 @@ public class Order extends OrderLineGroup {
 
     private Boolean dependenciesConstraintsHavePriority;
 
-    @NotNull
+    @NotNull(message = "order calendar not specified")
     private BaseCalendar calendar;
 
     public String getResponsible() {
@@ -118,19 +118,19 @@ public class Order extends OrderLineGroup {
 
     @SuppressWarnings("unused")
     @AssertTrue(message = "the order must have a init date")
-    private boolean theOrderMustHaveStartDate() {
+    private boolean checkConstraintOrderMustHaveStartDate() {
         return getInitDate() != null;
     }
 
     @SuppressWarnings("unused")
     @AssertTrue(message = "deadline must be after start date")
-    private boolean theDeadlineMustBeAfterStart() {
+    private boolean checkConstraintDeadlineMustBeAfterStart() {
         return !this.isDeadlineBeforeStart();
     }
 
     @SuppressWarnings("unused")
     @AssertTrue(message = "At least one HoursGroup is needed for each OrderElement")
-    private boolean atLeastOneHoursGroupForEachOrderElement() {
+    private boolean checkConstraintAtLeastOneHoursGroupForEachOrderElement() {
         for (OrderElement orderElement : this.getOrderElements()) {
             if (!orderElement.checkAtLeastOneHoursGroup()) {
                 return false;
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java
index 8d64c48e1..f04de5e8e 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java
@@ -54,7 +54,7 @@ import org.navalplanner.business.requirements.entities.IndirectCriterionRequirem
 import org.navalplanner.business.resources.entities.Criterion;
 public abstract class OrderElement extends BaseEntity {
 
-
+    @NotEmpty(message = "name not specified")
     private String name;
 
     private Date initDate;
@@ -73,6 +73,7 @@ public abstract class OrderElement extends BaseEntity {
 
     private Set<Label> labels = new HashSet<Label>();
 
+    @NotEmpty(message = "code not specified")
     private String code;
 
     private Set<CriterionRequirement> criterionRequirements = new HashSet<CriterionRequirement>();
@@ -243,7 +244,6 @@ public abstract class OrderElement extends BaseEntity {
 
     public abstract List<HoursGroup> getHoursGroups();
 
-    @NotEmpty
     public String getName() {
         return name;
     }
@@ -334,7 +334,6 @@ public abstract class OrderElement extends BaseEntity {
         this.code = code;
     }
 
-    @NotEmpty
     public String getCode() {
         return code;
     }
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineDTO.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineDTO.java
index 7c07c7eac..21e99b376 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineDTO.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineDTO.java
@@ -21,6 +21,7 @@
 package org.navalplanner.ws.orders.api;
 
 import java.util.Date;
+import java.util.HashSet;
 import java.util.Set;
 
 import javax.xml.bind.annotation.XmlElement;
@@ -39,7 +40,7 @@ public class OrderLineDTO extends OrderElementDTO {
 
     @XmlElementWrapper(name = "hours-groups")
     @XmlElement(name = "hours-group")
-    public Set<HoursGroupDTO> hoursGroups;
+    public Set<HoursGroupDTO> hoursGroups = new HashSet<HoursGroupDTO>();
 
     public OrderLineDTO() {
         super();
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineGroupDTO.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineGroupDTO.java
index c8165b237..55095bc1c 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineGroupDTO.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/api/OrderLineGroupDTO.java
@@ -20,6 +20,7 @@
 
 package org.navalplanner.ws.orders.api;
 
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
 import java.util.Set;
@@ -44,7 +45,7 @@ public class OrderLineGroupDTO extends OrderElementDTO {
             @XmlElement(name = "order-line", type = OrderLineDTO.class),
             @XmlElement(name = "order-line-group", type = OrderLineGroupDTO.class),
             @XmlElement(name = "order", type = OrderDTO.class) })
-    public List<OrderElementDTO> children;
+    public List<OrderElementDTO> children = new ArrayList<OrderElementDTO>();
 
     public OrderLineGroupDTO() {
         super();
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/impl/OrderElementConverter.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/impl/OrderElementConverter.java
index 0a6533526..0134237dc 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/impl/OrderElementConverter.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/orders/impl/OrderElementConverter.java
@@ -153,11 +153,17 @@ public final class OrderElementConverter {
 
                 ((Order) orderElement)
                         .setDependenciesConstraintsHavePriority(((OrderDTO) orderElementDTO).dependenciesConstraintsHavePriority);
+
                 List<BaseCalendar> calendars = Registry.getBaseCalendarDAO()
                         .findByName(((OrderDTO) orderElementDTO).calendarName);
+                BaseCalendar calendar;
                 if ((calendars != null) && (calendars.size() == 1)) {
-                    ((Order) orderElement).setCalendar(calendars.get(0));
+                    calendar = calendars.get(0);
+                } else {
+                    calendar = Registry.getConfigurationDAO()
+                            .getConfiguration().getDefaultCalendar();
                 }
+                ((Order) orderElement).setCalendar(calendar);
             } else { // orderElementDTO instanceof OrderLineGroupDTO
                 orderElement = OrderLineGroup.create();
             }
diff --git a/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/orders/OrderElementServiceTest.java b/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/orders/OrderElementServiceTest.java
new file mode 100644
index 000000000..45ebccc2e
--- /dev/null
+++ b/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/orders/OrderElementServiceTest.java
@@ -0,0 +1,182 @@
+/*
+ * This file is part of ###PROJECT_NAME###
+ *
+ * Copyright (C) 2009 Fundación para o Fomento da Calidade Industrial e
+ *                    Desenvolvemento Tecnolóxico de Galicia
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.navalplanner.web.test.ws.orders;
+
+import static org.hamcrest.CoreMatchers.anyOf;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.junit.Assert.assertThat;
+import static org.navalplanner.business.BusinessGlobalNames.BUSINESS_SPRING_CONFIG_FILE;
+import static org.navalplanner.web.WebappGlobalNames.WEBAPP_SPRING_CONFIG_FILE;
+import static org.navalplanner.web.test.WebappGlobalNames.WEBAPP_SPRING_CONFIG_TEST_FILE;
+
+import java.util.Date;
+import java.util.List;
+
+import javax.annotation.Resource;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.navalplanner.business.IDataBootstrap;
+import org.navalplanner.business.orders.daos.IOrderDAO;
+import org.navalplanner.business.orders.daos.IOrderElementDAO;
+import org.navalplanner.ws.common.api.ConstraintViolationDTO;
+import org.navalplanner.ws.common.api.InstanceConstraintViolationsDTO;
+import org.navalplanner.ws.orders.api.IOrderElementService;
+import org.navalplanner.ws.orders.api.OrderDTO;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.transaction.annotation.Transactional;
+
+/**
+ * Tests for {@link IOrderElementService}.
+ *
+ * @author Manuel Rego Casasnovas <mrego@igalia.com>
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(locations = { BUSINESS_SPRING_CONFIG_FILE,
+        WEBAPP_SPRING_CONFIG_FILE, WEBAPP_SPRING_CONFIG_TEST_FILE })
+@Transactional
+public class OrderElementServiceTest {
+
+    @Resource
+    private IDataBootstrap defaultAdvanceTypesBootstrapListener;
+
+    @Resource
+    private IDataBootstrap configurationBootstrap;
+
+    @Before
+    public void loadRequiredaData() {
+        defaultAdvanceTypesBootstrapListener.loadRequiredData();
+        configurationBootstrap.loadRequiredData();
+    }
+
+    @Autowired
+    private IOrderElementService orderElementService;
+
+    @Autowired
+    private IOrderDAO orderDAO;
+
+    @Autowired
+    private IOrderElementDAO orderElementDAO;
+
+    @Test
+    public void invalidOrderWithoutAttributes() {
+        int previous = orderDAO.getOrders().size();
+
+        OrderDTO orderDTO = new OrderDTO();
+
+        List<InstanceConstraintViolationsDTO> instanceConstraintViolationsList = orderElementService
+                .addOrder(orderDTO).instanceConstraintViolationsList;
+        assertThat(instanceConstraintViolationsList.size(), equalTo(1));
+
+        List<ConstraintViolationDTO> constraintViolations = instanceConstraintViolationsList
+                .get(0).constraintViolations;
+        // Mandatory fields: code, name. Check constraints:
+        // checkConstraintOrderMustHaveStartDate
+        assertThat(constraintViolations.size(), equalTo(3));
+
+        assertThat(orderDAO.getOrders().size(), equalTo(previous));
+    }
+
+    @Test
+    public void invalidOrderWithoutNameAndInitDate() {
+        int previous = orderDAO.getOrders().size();
+
+        OrderDTO orderDTO = new OrderDTO();
+        orderDTO.code = "order-code";
+
+        List<InstanceConstraintViolationsDTO> instanceConstraintViolationsList = orderElementService
+                .addOrder(orderDTO).instanceConstraintViolationsList;
+        assertThat(instanceConstraintViolationsList.size(), equalTo(1));
+
+        List<ConstraintViolationDTO> constraintViolations = instanceConstraintViolationsList
+                .get(0).constraintViolations;
+        // Mandatory fields: name. Check constraints:
+        // checkConstraintOrderMustHaveStartDate
+        assertThat(constraintViolations.size(), equalTo(2));
+
+        assertThat(orderDAO.getOrders().size(), equalTo(previous));
+    }
+
+    @Test
+    public void invalidOrderWithoutCodeAndInitDate() {
+        int previous = orderDAO.getOrders().size();
+
+        OrderDTO orderDTO = new OrderDTO();
+        orderDTO.name = "Order name";
+
+        List<InstanceConstraintViolationsDTO> instanceConstraintViolationsList = orderElementService
+                .addOrder(orderDTO).instanceConstraintViolationsList;
+        assertThat(instanceConstraintViolationsList.size(), equalTo(1));
+
+        List<ConstraintViolationDTO> constraintViolations = instanceConstraintViolationsList
+                .get(0).constraintViolations;
+        // Mandatory fields: code. Check constraints:
+        // checkConstraintOrderMustHaveStartDate
+        assertThat(constraintViolations.size(), equalTo(2));
+
+        assertThat(orderDAO.getOrders().size(), equalTo(previous));
+    }
+
+    @Test
+    public void invalidOrderWithoutCodeAndName() {
+        int previous = orderDAO.getOrders().size();
+
+        OrderDTO orderDTO = new OrderDTO();
+        orderDTO.initDate = new Date();
+
+        List<InstanceConstraintViolationsDTO> instanceConstraintViolationsList = orderElementService
+                .addOrder(orderDTO).instanceConstraintViolationsList;
+        assertThat(instanceConstraintViolationsList.size(), equalTo(1));
+
+        List<ConstraintViolationDTO> constraintViolations = instanceConstraintViolationsList
+                .get(0).constraintViolations;
+        // Mandatory fields: code, name
+        assertThat(constraintViolations.size(), equalTo(2));
+        for (ConstraintViolationDTO constraintViolationDTO : constraintViolations) {
+            assertThat(constraintViolationDTO.fieldName, anyOf(
+                    equalTo("Order::code"), equalTo("Order::name")));
+        }
+
+        assertThat(orderDAO.getOrders().size(), equalTo(previous));
+    }
+
+    @Test
+    public void validOrder() {
+        String code = "order-code";
+        int previous = orderElementDAO.findByCode(code).size();
+
+        OrderDTO orderDTO = new OrderDTO();
+        orderDTO.name = "Order name";
+        orderDTO.code = code;
+        orderDTO.initDate = new Date();
+
+        List<InstanceConstraintViolationsDTO> instanceConstraintViolationsList = orderElementService
+                .addOrder(orderDTO).instanceConstraintViolationsList;
+        assertThat(instanceConstraintViolationsList.size(), equalTo(0));
+
+        assertThat(orderElementDAO.findByCode(code).size(),
+                equalTo(previous + 1));
+    }
+
+}