如何验证是否存在外键输入? [英] How to validate if a foreign key entry exists?

问题描述

我的Customer表中有外键.

@JoinColumn(name = "DISCOUNT_CODE", referencedColumnName = "DISCOUNT_CODE")
@ManyToOne(optional = false)
private DiscountCode discountCode;

我有一个包含此表所有字段的表单(包括外键discountCode及其对另一个表的描述).

I have a form that contains all fields of this table (including the foreign key discountCode and its description from the other table).

在用户输入外键表中不存在的输入的情况下，我希望能够显示此外键不存在的消息. 当我对该字段进行模糊处理时，我将从表中检索其描述.当用户模糊处理无效字段并且表中不存在该字段时，如何显示错误消息?

I want to be able to show a message that this foreign key does not exist in case that the user entered an input that does not exist in the foreign key table. When I onblur this field, then I'm retriving its description from the table. How can I show the error message of invalid field when the user onblurs it and it does not exist in the table?

推荐答案

您需要的是Validator.它应该看起来像这样:

What you need is a Validator. It should look like this:

@ManagedBean
@RequestScoped
public class DiscountCodeValidator implements Validator {
    @EJB
    private MrBean mrBean;

    @Override
    public void validate(FacesContext context, UIComponent component, Object value) throws ValidatorException {
        String discountCode = (String) value;

        if (!mrBean.checkDiscountCodeExistence(discountCode)) {
            throw new ValidatorException(new FacesMessage("This code is not valid!"));
        }
    }
}

在您的.xhtml文件中，您可以按以下方式声明此验证器:

In your .xhtml file, you can declare this validator as following:

<h:inputText id="discountCode" value="#{someBean.discountCode}" 
             validator="#{discountCodeValidator}" 
             required="true" requiredMessage="Discount code is required.">
   <f:ajax event="blur" render="discountMsg" />
</h:inputText>
<h:message for="discountCode" id="discountMsg"/>

要注意的一件事是，我假设您将注入一个EJB以使用checkDiscountCodeExistence()函数检查折扣代码的存在.因此，我将上述验证器注释为@ManagedBean.如果不需要注入任何EJB，则可以使用@FacesValidator注释验证器.

One thing to note is I assume that you would inject an EJB to check the existence of the discount code with the checkDiscountCodeExistence() function. Hence, I annotated the above Validator as a @ManagedBean. If you don't need to inject any EJBs, you can annotate the Validator with @FacesValidator.

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