thymeleaf 无法将 java.lang.String 类型的属性值转换为所需的 java.util.List 类型 [英] thymeleaf Failed to convert property value of type java.lang.String to required type java.util.List

问题描述

我是 Spring 和 Spring Boot 的新手，正在阅读一本充满缺失信息的书.

I am new to Spring and Spring Boot and am working through a book that is full of missing information.

我有一个炸玉米饼课:

public class Taco {

    ...

    @Size(min=1, message="You must choose at least 1 ingredient")
    private List<Ingredient> ingredients;

    ...
}

正如你所看到的 ingredients 是 List 类型，这就是问题所在，它曾经是 List 类型code> 但那是在我开始在数据库中保存数据之前，现在它必须是 List 打破了整个事情.

As you can see ingredients is of type List<Ingredient> and that is the problem, it used to be of type List<String> but that was before I started saving data in the database, now it must be List<Ingredient> which breaks the whole thing.

在控制器中，我有以下内容(除其他外，我认为这是解决手头问题唯一需要的代码，但如果您需要更多，请告诉我):

In the contoller I have the following (among other things, I think this is the only required code for the problem at hand but if you need more let me know):

@ModelAttribute
    public void addIngredientsToModel(Model model) {
        List<Ingredient> ingredients = new ArrayList<>();
        ingredientRepo.findAll().forEach(i -> ingredients.add(i));

        Type[] types = Ingredient.Type.values();
        for (Type type : types) {
            model.addAttribute(type.toString().toLowerCase(), filterByType(ingredients, type));
        }
    }

private List<Ingredient> filterByType(List<Ingredient> ingredients, Type type) {
        return ingredients
                    .stream()
                    .filter(x -> x.getType()
                    .equals(type))
                    .collect(Collectors.toList());
    }

最后在我的百里香文件中:

And finally in my thymeleaf file I have:

<span class="text-danger" 
                th:if="${#fields.hasErrors('ingredients')}" 
                th:errors="*{ingredients}">
            </span>

导致错误的原因:

thymeleaf Failed to convert property value of type java.lang.String to required type java.util.List

再次，当private List成分; 是 private List成分;它起作用了，但现在它必须是private List成分;因为它在数据库中的保存方式，但此时它坏了，如何修复它?

Once again, when private List<Ingredient> ingredients; was private List<String> ingredients; it worked, but now it must be private List<Ingredient> ingredients; because of the way it is saved in the database but it breaks at this point, how to fix it?

推荐答案

我遇到了同样的问题，我们需要一个转换器.

I met the same problem, what we need here is a converter.

package tacos.web;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.convert.converter.Converter;
import org.springframework.stereotype.Component;

import tacos.Ingredient;
import tacos.data.IngredientRepository;

@Component
public class IngredientByIdConverter implements Converter<String, Ingredient> {

private IngredientRepository ingredientRepo;

@Autowired
public IngredientByIdConverter(IngredientRepository ingredientRepo) {
    this.ingredientRepo = ingredientRepo;
}

@Override
public Ingredient convert(String id) {
    return ingredientRepo.findOne(id);
}

}

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