POSTing data with many to one relationship using Thymeleaf

Question

I have a simple model class Product which exhibits a many to one relationship with ProductCategory:

Product class:

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Answer 1

Note that I have changed the form method to POST.

From thymeleafs perspective I can assure the below code should work.

<form method="POST" th:action="@{/product/save}" th:object="${newProduct}">
    ....
    <select th:field="*{category}" class="form-control">
       <option th:each="category: ${productCategories}" th:value="${category.id}" th:text="${category.name}"></option>
    </select>

Provided that your controller looks like this.

@RequestMapping(value = "/product/save")
public String create(Model model) {
    model.addAttribute("productCategories", productCategoryService.findAll());
    model.addAttribute("newproduct", new Product()); //or try to fetch an existing object
    return '<your view path>';
}

@RequestMapping(value = "/product/save", method = RequestMethod.POST)
public String create(Model model, @Valid @ModelAttribute("newProduct") Product newProduct, BindingResult result) {
    if(result.hasErrors()){
        //error handling  
        ....
    }else {
        //or calling the repository to save the newProduct
        productService.save(newProduct);
        ....
    }
}

Update

Your models should have proper getters and setters with the correct names. For example, for the property category You should have,

public ProductCategory getCategory(){
    return category;
}

public void setCategory(productCategory category){
    this.category = category;
}

NOTE - I have not compiled this code, I got it extracted from my current working project and replace the names with your class names