+ get(Author/Publisher/Category/Book)

src/main/java/de/hsel/itech/db/Database.java

@@ -1,16 +1,26 @@
 package de.hsel.itech.db;
 
 import de.hsel.itech.config.Configuration;
+import de.hsel.itech.db.pojo.Author;
+import de.hsel.itech.db.pojo.Book;
+import de.hsel.itech.db.pojo.Category;
+import de.hsel.itech.db.pojo.Publisher;
 import org.jetbrains.annotations.Nullable;
 import org.mariadb.jdbc.MariaDbPoolDataSource;
 
 import java.io.BufferedReader;
 import java.io.FileReader;
 import java.io.IOException;
+import java.net.URL;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
+import java.time.Year;
+import java.util.AbstractMap;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
 
 /**
  *
@@ -41,7 +51,9 @@ public class Database {
 
             Connection connection = getConnection();
             assert connection != null;
-            try(BufferedReader br = new BufferedReader(new FileReader(getClass().getClassLoader().getResource("database.sql").getFile()))) {
+            URL file = getClass().getClassLoader().getResource("database.sql");
+            assert file != null;
+            try(BufferedReader br = new BufferedReader(new FileReader(file.getFile()))) {
                 for (String line = br.readLine(); line != null; line = br.readLine()) {
                     PreparedStatement statement = connection.prepareStatement(line);
                     statement.executeUpdate();
@@ -88,8 +100,141 @@ public class Database {
 
     }
 
+    @Nullable
+    private Map.Entry<ResultSet, Connection> getResultSet(long id, String table) {
+        Connection connection = getConnection();
+        try{
+            assert connection != null;
+            PreparedStatement statement = connection.prepareStatement("SELECT * FROM ? WHERE ID = ?");
+            statement.setString(1, table);
+            statement.setLong(2, id);
+            ResultSet resultSet = statement.executeQuery();
+            if(resultSet.next()) {
+                return new AbstractMap.SimpleEntry<>(resultSet, connection);
+            }
+            return null;
+
+        }catch (SQLException ex) {
+            ex.printStackTrace();
+        }
+        return null;
+    }
+
+    @Nullable
+    private Map.Entry<List<ResultSet>, Connection> getResultSets(long id, String table, String column) {
+        Connection connection = getConnection();
+        try {
+            assert connection != null;
+            PreparedStatement statement = connection.prepareStatement("SELECT * FROM ? WHERE ? = ?");
+            statement.setString(1, table);
+            statement.setString(2, column);
+            statement.setLong(3, id);
+
+            ResultSet resultSet = statement.executeQuery();
+
+            Map.Entry<List<ResultSet>, Connection> entry = new AbstractMap.SimpleEntry<>(new ArrayList<>(), connection);
+            while(resultSet.next()) {
+                entry.getKey().add(resultSet);
+            }
+            return entry;
 
 
+        }catch (SQLException ex) {
+            ex.printStackTrace();
+        }
+        return null;
+    }
 
 
+    @Nullable
+    public Author getAuthor(long id) {
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "author");
+        assert entry != null;
+
+        ResultSet rs = entry.getKey();
+        Author author = null;
+        try {
+            author = new Author(rs.getLong("id"), rs.getString("name"));
+            entry.getValue().close();
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+        return author;
+    }
+
+    @Nullable
+    public Category getCategory(long id) {
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "category");
+        assert entry != null;
+
+        ResultSet rs = entry.getKey();
+        Category category = null;
+        try {
+            category = new Category(rs.getLong("id"), rs.getString("name"), rs.getString("image"));
+            entry.getValue().close();
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+        return category;
+    }
+
+    @Nullable
+    public Publisher getPublisher(long id) {
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "category");
+        assert entry != null;
+
+        ResultSet rs = entry.getKey();
+        Publisher publisher = null;
+        try {
+            publisher = new Publisher(rs.getLong("id"), rs.getString("name"));
+            entry.getValue().close();
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+        return publisher;
+    }
+
+    @Nullable
+    private List<Integer> getAuthors(long id) {
+         Map.Entry<List<ResultSet>, Connection> entry = getResultSets(id, "author_book", "book");
+         assert entry != null;
+        try {
+            List<Integer> list = new ArrayList<>();
+            for(ResultSet rs : entry.getKey()) {
+                list.add(rs.getInt("author"));
+            }
+            entry.getValue().close();
+            return list;
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+        return null;
+    }
+
+    @Nullable
+    public Book getBook(long id) {
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "book");
+        assert entry != null;
+
+        ResultSet rs = entry.getKey();
+        Book book = null;
+        try {
+            Category category = getCategory(rs.getLong("category"));
+            Publisher publisher = getPublisher(rs.getLong("publisher"));
+            List<Integer> authorIds = getAuthors(id);
+            assert authorIds != null;
+            List<Author> authors = new ArrayList<>();
+            for(int i : authorIds) {
+                Author author = getAuthor(i);
+                assert author != null;
+                authors.add(author);
+            }
+            book = new Book(rs.getLong("id"), authors, publisher, category, rs.getString("title"), Year.of(rs.getInt("year")), rs.getInt("price"), rs.getString("description"), rs.getString("image"));
+            entry.getValue().close();
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+        return book;
+    }
+
 }

src/main/java/de/hsel/itech/db/pojo/Book.java

@@ -4,6 +4,7 @@ import lombok.AllArgsConstructor;
 import lombok.Data;
 
 import java.time.Year;
+import java.util.List;
 
 /**
  * @author Johannes Theiner
@@ -15,8 +16,8 @@ import java.time.Year;
 @AllArgsConstructor
 public class Book {
 
-    private int isbn;
+    private long isbn;
-    private Author author;
+    private List<Author> authors;
     private Publisher publisher;
     private Category category;
     private String title;

src/main/java/de/hsel/itech/db/pojo/Category.java

@@ -13,7 +13,7 @@ import lombok.Data;
 @AllArgsConstructor
 public class Category {
 
-    private int id;
+    private long id;
     private String name;
     private String image;
 }