问题
Is there anything like AutoPopulatingList
but for Set
?
The data that I want to show is an association that uses Set
.
public class Employer implements java.io.Serializable {
private Set<Employee> employees = new HashSet();
}
I've tried using AutoPopulatingList
but in that case I have to use List
in hibernate which needs me to specify list-index
using Employee.employeeId
and whenever I retrieve the employees
through Employee
later the list would have spaces between element (null
elements) depending on the Employee.employeeId
.
I need to auto-populate the collection because I need to generate the employees
dynamically while creating the Employer
.
I got the following when I use plain Set
:
org.springframework.beans.InvalidPropertyException: Invalid property 'employees[0]' of bean class [model.Employer]: Cannot get element with index 0 from Set of size 0, accessed using property path 'employees[0]'
Is there any other solution?
Edit
I'm trying to implement dynamic form
回答1:
You can not use Set
as a binding target in MVC because it is not possible to create property path for its items.
What you should use
You should use Map<Integer, YourType>
when building dynamic forms. What we have implemented many times (so I know it is working) is this:
- a simple number sequence is used as keys without any connection to the actual items
- the key sequence is always increasing but doesn't need to be continuous (e.g. in case user will delete the second item, you will end up with
1, 3, 4, ...
) - if you want to add another item, you just find the highest number and then add form indexed with
maxIndex + 1
(always increasing sequence) - the
Map
implementation MUST BE instance ofLinkedHashMap
so that the iteration order is preserved (Spring is creating this implementation by default if aMap
field needs to be autopopulated) - the
Map
must be part of some parent form object (i.e. you can not haveMap
as the top form object) so that Spring is able to infer the generic types from the property getter
View and JavaScript implementation example
There are many ways how you can work with this. For example we have a special template subform, which is used when we need to dynamically add another subform. This approach is probably a bit more complex to follow:
<form:form action="${formUrl}" method="post" modelAttribute="organizationUsersForm">
<%-- ... other fields ... --%>
<div id="userSubforms">
<c:forEach items="${organizationUsersForm.users.entrySet()}" var="subformEntry">
<div data-subform-key="${subformEntry.key}">
<spring:nestedPath path="users['${subformEntry.key}']">
<%@ include file="user-subform.jspf" %>
</spring:nestedPath>
</div>
</c:forEach>
</div>
<button onclick="addSubform(jQuery('#userSubforms'), 'users', 'user', 'userTemplate');">ADD ANOTHER USER</button>
<%-- other form fields, submit, etc. --%>
</form:form>
<div class="hide" data-subform-template="user">
<spring:nestedPath path="userTemplate">
<%@ include file="user-subform.jspf" %>
</spring:nestedPath>
</div>
<script>
function addSubform(subformContainer, subformPath, templateName, templatePath) {
// Find the sequence number for the new subform
var existingSubforms = subformContainer.find("[data-subform-key]");
var subformIndex = (existingSubforms.length != 0) ?
parseInt(existingSubforms.last().attr("data-subform-key"), 10) + 1 : 0;
// Create new subform based on the template
var subform = jQuery('<div data-subform-key="' + subformIndex + '" />').
append(jQuery("[data-subform-template=" + templateName + "]").children().clone(true));
// Don't forget to update field names, identifiers and label targets
subform.find("[name]").each(function(node) {
this.name = subformPath + "["+ subformIndex +"]." + this.name;
});
subform.find("[for^=" + templatePath + "]").each(function(node) {
this.htmlFor = this.htmlFor.replace(templatePath + ".", subformPath + "["+ subformIndex +"].");
});
subform.find("[id^=" + templatePath + "]").each(function(node) {
this.id = this.id.replace(templatePath + ".", subformPath + "["+ subformIndex +"].");
});
// Add the new subform to the form
subformContainer.append(subform);
}
</script>
Now you can ask "How can user delete a subform"? This is pretty easy if the subform JSPF contains:
<button onclick="jQuery(this).parents('[data-subform-key]').remove();">DELETE USER</button>
回答2:
Set isn't an indexed collection, you can only bind indexed collections or arrays. You might try with a LinkedHashSet (that one has a guaranteed order, whereas HashSet doesn't) or use List implementations for binding the values.
回答3:
"Cannot get element with index 0".. sets are not indexed based to begin with..
why don't you use LazyList of Employee.. as correctly pointed out by @PavelHoral we don't need to use LazyList as Spring handles it.. a simple List initialization (like new ArrayList()) would do, albeit with the possibility of having spaces(nulls) when user submits non-continuous elements.
private List<Employee> employees = new ArrayList<Employee>();
来源:https://stackoverflow.com/questions/17002027/auto-populating-set