Why am I getting this error, regarding Hibernate on my RESTful API?

The error in question: jakarta.servlet.ServletException: java.lang.IllegalArgumentException: org.hibernate.query.SemanticException: Could not interpret path expression ‘brand_id’;

I am new to hibernate and REST Api design, so it eludes me why I get this error, I have tried so many things. "brand_id" is the name of the foreign key column in my database, you know what, lemme show you.

Here is my exposed GET endpoint:

    `@GET
@Path("/{brandID}/products")
@Produces(MediaType.APPLICATION_JSON)
public List<ProductEntity> getProductsByBrand(@PathParam("brandID") int brandID) {
    List<ProductEntity> productList = productsService.getProductsByBrand(brandID);
    return productList;
}`

Here is my ProductsService class:

`public class ProductsService {
private final ProductsDAO dao = new ProductsDAO();

public List<ProductEntity> getProductsByBrand(int brandID) {
    List<ProductEntity> productList = dao.getProductsByBrand(brandID);
    return productList;
    
}

}`

And here is the ProductsDAO class:

 `public class ProductsDAO {
private final SessionFactory factory = new Configuration().configure("hibernate.cfg.xml").addAnnotatedClass(ProductEntity.class).addAnnotatedClass(BrandEntity.class) // since we are defining a foreign key in the ProductEntity, we are required to add the BrandEntity class as an Annotated Class                                       .buildSessionFactory();

public List<ProductEntity> getProductsByBrand(int brandID) {
    Session session = factory.getCurrentSession();
    session.beginTransaction();
    
    String hql = "from products where brand_id = '" + brandID + "'";
    Query query = session.createQuery(hql);
    
    List<ProductEntity> productList = query.getResultList();
    return productList;
    
}

}`

And of course, my ProductEntity class:

`@Entity(name = "products")
@Table(name = "products")
public class ProductEntity {
@Id
@Column(name = "product_id")
private int productId;

// Essentially, this is how you specify a Foreign Key to hibernate
@ManyToOne(targetEntity = BrandEntity.class) // Specifies that this column has a multiplicity defined relationship with other entities, such as tables. It cannot be used on a primitve data type, only a entity class type, in addition, the column annotation cannot be used in conjunction with it.
@JoinColumn(name = "brand_id")
private BrandEntity brandEntity;

@Column(name = "product_name")
private String productName;

@Column(name = "category")
private String category;

@Column(name = "cost")
private String cost;

public ProductEntity() {
    
}

public ProductEntity(int productId, BrandEntity brandEntity, String productName, String category, String cost) {
    this.productId = productId;
    this.brandEntity = brandEntity;
    this.productName = productName;
    this.category = category;
    this.cost = cost;
}

public int getProductId() {
    return productId;
}

public void setProductId(int productId) {
    this.productId = productId;
}

public BrandEntity getBrandEntity() {
    return brandEntity;
}

public void setBrandEntity(BrandEntity brandEntity) {
    this.brandEntity = brandEntity;
}

public String getProductName() {
    return productName;
}

public void setProductName(String productName) {
    this.productName = productName;
}

public String getCategory() {
    return category;
}

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

public String getCost() {
    return cost;
}

public void setCost(String cost) {
    this.cost = cost;
}

}`

If anyone can shed any light on this issue, i would be sincerely grateful.

Note: I receive this error when sending a GET request to the URI defined as : http://localhost:8008/104_-_RESTApp_ManyToOne_Mapping_In_Hibernate/showroom/brands/2/products, for example.

>Solution :

The error message "Could not interpret path expression ‘brand_id’" is indicating that Hibernate is having trouble understanding what you’re trying to do with the "brand_id" in your query.

It looks like there is an issue with the way you are querying for products based on the brand id. Your query string "from products where brand_id = ‘" + brandID + "’" is specifying a condition on the "brand_id" column, but in your ProductEntity class, the name of the field for the brand id is "brandEntity", not "brand_id".

To resolve this issue, you should modify your query to use the correct field name:

String hql = "from products where brandEntity.brandId = :brandID";
Query query = session.createQuery(hql);
query.setParameter("brandID", brandID);

Also, since the brand id is an integer, it’s a good idea to use the setParameter method to bind the value, rather than concatenating it into the query string, which can make your application vulnerable to SQL injection attacks.