Reading data from a Cursor

suggest change

Here is an example of a method that would live inside a SQLiteOpenHelper subclass. It uses the searchTerm String to filter the results, iterates through the Cursor’s contents, and returns those contents in a List of Product Objects.

First, define the Product POJO class that will be the container for each row retrieved from the database:

public class Product {
  long mId;
  String mName;
  String mDescription;
  float mValue;
  public Product(long id, String name, String description, float value) {
    mId = id;
    mName = name;
    mDescription = description;
    mValue = value;
  }
}

Then, define the method that will query the database, and return a List of Product Objects:

public List<Product> searchForProducts(String searchTerm) {
    
    // When reading data one should always just get a readable database.
    final SQLiteDatabase database = this.getReadableDatabase();

    final Cursor cursor = database.query(
            // Name of the table to read from
            TABLE_NAME,

            // String array of the columns which are supposed to be read
            new String[]{COLUMN_NAME, COLUMN_DESCRIPTION, COLUMN_VALUE},

            // The selection argument which specifies which row is read.
            // ? symbols are parameters.
            COLUMN_NAME + " LIKE ?",

            // The actual parameters values for the selection as a String array.
            // ? above take the value from here
            new String[]{"%" + searchTerm + "%"},

            // GroupBy clause. Specify a column name to group similar values
            // in that column together.
            null,

            // Having clause. When using the GroupBy clause this allows you to
            // specify which groups to include.
            null,

            // OrderBy clause. Specify a column name here to order the results
            // according to that column. Optionally append ASC or DESC to specify
            // an ascending or descending order.
            null
    );

    // To increase performance first get the index of each column in the cursor
    final int idIndex = cursor.getColumnIndex(COLUMN_ID);
    final int nameIndex = cursor.getColumnIndex(COLUMN_NAME);
    final int descriptionIndex = cursor.getColumnIndex(COLUMN_DESCRIPTION);
    final int valueIndex = cursor.getColumnIndex(COLUMN_VALUE);

    try {

        // If moveToFirst() returns false then cursor is empty
        if (!cursor.moveToFirst()) {
            return new ArrayList<>();
        }

        final List<Product> products = new ArrayList<>();

        do {

            // Read the values of a row in the table using the indexes acquired above
            final long id = cursor.getLong(idIndex);
            final String name = cursor.getString(nameIndex);
            final String description = cursor.getString(descriptionIndex);
            final float value = cursor.getFloat(valueIndex);

            products.add(new Product(id, name, description, value));

        } while (cursor.moveToNext());

        return products;

    } finally {
        // Don't forget to close the Cursor once you are done to avoid memory leaks.
        // Using a try/finally like in this example is usually the best way to handle this
        cursor.close();

        // close the database
        database.close();
    }
}

Found a mistake? Have a question or improvement idea? Let me know.

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