# Persisting data

> SQLite (SqliteDb/SqliteCursor) behind a repository — 1-based bind, 0-based getters.

Source: https://crossfly.dev/docs/learn/persisting-data — CrossFly documentation. Full docs as one file: https://crossfly.dev/llms-full.txt

# 9. Persisting data

> **What you will learn:** actually writing to disk with SQLite, behind a repository.
> **Prerequisites:** [Loading data](/docs/learn/loading-data).

## Complete example (copy, paste and run)
A SQLite repository (facade) isolating the SQL, called **off the paint thread** in a `Thread`, and the
result displayed via `Component.onUI`. 1-based bind, 0-based cursor, try-with-resources. Compiles as is.
```java
package com.exemplo;

import java.util.*;
import dev.crossfly.ui.*;
import dev.crossfly.ui.layout.*;
import dev.crossfly.sqlite.*;

public class MainWindow extends Window
{
   private final TarefaRepositorySQLite repo = new TarefaRepositorySQLite();
   private final Component listaBox = new Component();

   @Override
   public void onShow() throws Exception
   {
      super.onShow();
      setLayout(new VerticalLayout());

      Button add = new Button("Inserir e recarregar");
      add.onAction(c -> new Thread(() -> {               // I/O off the paint thread
         repo.inserir("Tarefa " + System.currentTimeMillis());
         var dados = repo.listar();
         Component.onUI(() -> renderizar(dados));         // back to the paint thread
      }).start());
      add(LAY_AUTO, add);

      listaBox.setLayout(new VerticalLayout());
      add(LAY_FILL, listaBox);

      new Thread(() -> {                                  // initial load in background
         var dados = repo.listar();
         Component.onUI(() -> renderizar(dados));
      }).start();
   }

   private void renderizar(List<Tarefa> dados)
   {
      listaBox.removeAll();
      for (Tarefa t : dados) listaBox.add(LAY_AUTO, new Label(t.id + " · " + t.titulo));
      listaBox.setValidLayout(false);
      Component.repaint();
   }
}

class Tarefa
{
   final int id; final String titulo;
   Tarefa(int id, String titulo) { this.id = id; this.titulo = titulo; }
}

class TarefaRepositorySQLite
{
   private static final String DB = "tarefas.db";

   public TarefaRepositorySQLite()
   {
      try (SqliteDb db = SqliteDb.open(DB)) {
         db.exec("CREATE TABLE IF NOT EXISTS tarefa(id INTEGER PRIMARY KEY, titulo TEXT, feito INTEGER)");
      } catch (Exception e) { Debug.handle(e); }
   }

   public List<Tarefa> listar()
   {
      List<Tarefa> out = new ArrayList<>();
      try (SqliteDb db = SqliteDb.open(DB);
           SqliteCursor c = db.query("SELECT id, titulo FROM tarefa ORDER BY id")) {
         while (c.next())                                 // getters 0-based
            out.add(new Tarefa(c.getInt(0), c.getString(1)));
      } catch (Exception e) { Debug.handle(e); }
      return out;
   }

   public void inserir(String titulo)
   {
      try (SqliteDb db = SqliteDb.open(DB)) {
         db.execute("INSERT INTO tarefa(titulo, feito) VALUES(?, ?)", titulo, 0);   // bind 1-based
      } catch (Exception e) { Debug.handle(e); }
   }
}
```
> The snippets below show **only the core** (what goes inside `onShow()`). To run them, place them in the `MainWindow` skeleton above.

## The `dev.crossfly.sqlite` module
`SqliteDb`/`SqliteStmt`/`SqliteCursor` — all `AutoCloseable` (use try-with-resources) and run
**off the paint thread**.

## A repository (facade)
Isolate the SQL in a class; the UI never speaks SQL directly:
```java
public class TarefaRepositorySQLite {
   private static final String DB = "tarefas.db";

   public TarefaRepositorySQLite() {
      try (SqliteDb db = SqliteDb.open(DB)) {
         db.exec("CREATE TABLE IF NOT EXISTS tarefa(id INTEGER PRIMARY KEY, titulo TEXT, feito INTEGER)");
      } catch (Exception e) { Debug.handle(e); }
   }

   public List<Tarefa> listar() {
      List<Tarefa> out = new ArrayList<>();
      try (SqliteDb db = SqliteDb.open(DB);
           SqliteCursor c = db.query("SELECT id, titulo FROM tarefa ORDER BY id")) {
         while (c.next())                                   // getters 0-based
            out.add(new Tarefa(c.getInt(0), c.getString(1)));
      } catch (Exception e) { Debug.handle(e); }
      return out;
   }

   public void inserir(String titulo) {
      try (SqliteDb db = SqliteDb.open(DB)) {
         db.execute("INSERT INTO tarefa(titulo, feito) VALUES(?, ?)", titulo, 0);   // bind 1-based
      } catch (Exception e) { Debug.handle(e); }
   }
}
```

## ⚠️ The two golden rules
| Operation | Base |
|---|---|
| parameter **bind** (`?`) | **1-based** |
| column **getter** (cursor) | **0-based** |

For bulk writes, use `transaction(...)`/`bulkInsert(...)`. For sensitive data, open with a key
(`SqliteDb.open(file, key)`, see [Security](/docs/best-practices/seguranca)).

## What you build in this step
The **`TarefaRepositorySQLite`** — the app now **survives restarts**.

## Recap
SQLite via a repository, try-with-resources, off the paint thread; **1-based bind, 0-based cursor**;
transactions/bulk for batches.

## Next steps
→ [Making it responsive](/docs/learn/making-it-responsive)

## See also
- [Persistence with SQLite](/docs/data-and-services/storage-sqlite) · Canonical source: Chapter 23 — SQLite