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How to Group ResultSet in Map By Objects (Java, JDBC)




Hi) I have two classes that I need to create, getting some data for them from dB:

@ data
Public Class Product Implements Replication & LT; Product & GT; {
  Private Long ID;
  Private String Name;
  Private Long Priceincents;
  Private int rarate;
  Public Product (String Name, Long Preincents, Int Rate) {
    this.name = Name;
    this.priceincents = PriceinCents;
    this.rate = rate;
  Public Product Copy () {
    Return New Product (ID, NAME, PRIINCENTS, RATE);
@ data
Public Class Category Implements Replication & LT; Category & GT; {
  Private Long ID;
  Private String Title;
  Private List & lt; Product & GT; Products;
  Public Category Copy () {
    List & lt; Product & GT; CopiedProducts = this.Products.stream ()
        .map (Product :: Copy)
        .collect (collectors.tolist ());

I’ll get them so — & gt; select * from Products P Join Categories C ON P.Category_id = C.category_id

After executing the query, they fall into the resultset. How can I handle ResultSet to do somehow from it Stream, ultimately, creating all objects? Maybe there is an option at least somehow group the result to provide where one category ends and the other starts?

For example, the desired result would be Map & Lt; Category, List & LT; Product & GT; & GT;

BD scripts:

create database shop;
Create Table Categories (
Category_id bigint not null auto_increment primary key
Category_name Varchar (100) Not NULL
    Product_ID Bigint Not Null Auto_Increment Primary Key,
    Product_Name Varchar (100) Not NULL,
    Price_IN_CENTS bigint,
    Category_id Bigint Not Null,
      Constraint fk_products_categories.
        Foreign Key (Category_id) References Categories (Category_ID)

Answer 1

Question decided. If someone helps, nothing to implement (spliters and other):

public list & lt; Category & gt; Findall () {
    String Query = "Select * from Categories C join Products P on C.category_id = p.category_id";
    MAP & LT; Category, List & LT; Product & GT; & GT; GroupedCategories = New Linkedhashmap & lt; & gt; ();
    TRY (Connection Connection = ConnectionProvider.getConnection ();
       Statement statement = connection.createTatement ();
       ResultSet ResultSet = Statement.ExecuteQuery (Query)) {
      While (resultset.next ()) {
        Category Category = New Category ();
        Category.Setid (resultset.getlong ("Category_ID"));
        Category.Settitle (resultset.getstring ("Category_name"));
        if (! groupedcategories.containskey (Category)) {
          GroupedCategories.Put (Category, New ArrayList & LT; & GT; ());
        Product Product = NEW Product ();
        Product.Setid (resultset.getlong ("product_id"));
        Product.Setrate (ResultSet.getint ("RATE"));
        Product.setName (resultset.getString ("Product_Name"));
        Product.SetPriceInCents (ResultSet.getlong ("Price_in_Cents"));
        GroupedCategories.get (Category) .add (Product);
    } Catch (SQLEXCEPTION E) {
      Throw New DatabaseException (E.getMessage ());
    Return GroupedCategories.EntrySet (). Stream ()
        .peek (entry - & gt; entry.getkey (). setProducts (entry.getvalue ()))
        .map (map.ENTRY :: Getkey)
        .collect (collectors.tolist ());

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