Question

考虑使用以下方法从一些数据结构（InteractionNetwork）读取数据，并使用SQLite-JDBC dirver将它们写入SQLite数据库中的表：

private void loadAnnotations(InteractionNetwork network) throws SQLException {
    PreparedStatement insertAnnotationsQuery = 
        connection.prepareStatement(
        "INSERT INTO Annotations(GOId, ProteinId, OnthologyId) VALUES(?, ?, ?)");
    PreparedStatement getProteinIdQuery = 
        connection.prepareStatement(
        "SELECT Id FROM Proteins WHERE PrimaryUniProtKBAccessionNumber = ?");
    connection.setAutoCommit(false);
    for(common.Protein protein : network.get_protein_vector()) {
        /* Get ProteinId for the current protein from another table and
           insert the value into the prepared statement. */
        getProteinIdQuery.setString(1, protein.get_primary_id());
        ResultSet result = getProteinIdQuery.executeQuery();
        result.next();
        insertAnnotationsQuery.setLong(2, result.getLong(1));
        /* Extract all the other data and add all the tuples to the batch. */
    }
    insertAnnotationsQuery.executeBatch();
    connection.commit();
    connection.setAutoCommit(true);
}

此代码工作正常，程序运行大约30秒，平均占用80毫米空间。因为代码看起来很丑，我想重构它。我做的第一件事就是将getProteinIdQuery的声明移到循环中：

private void loadAnnotations(InteractionNetwork network) throws SQLException {
    PreparedStatement insertAnnotationsQuery = 
        connection.prepareStatement(
        "INSERT INTO Annotations(GOId, ProteinId, OnthologyId) VALUES(?, ?, ?)");
    connection.setAutoCommit(false);
    for(common.Protein protein : network.get_protein_vector()) {
        /* Get ProteinId for the current protein from another table and
           insert the value into the prepared statement. */
        PreparedStatement getProteinIdQuery = // <--- moved declaration of statement here
            connection.prepareStatement(
            "SELECT Id FROM Proteins WHERE PrimaryUniProtKBAccessionNumber = ?");
        getProteinIdQuery.setString(1, protein.get_primary_id());
        ResultSet result = getProteinIdQuery.executeQuery();
        result.next();
        insertAnnotationsQuery.setLong(2, result.getLong(1));
        /* Extract all the other data and add all the tuples to the batch. */
    }
    insertAnnotationsQuery.executeBatch();
    connection.commit();
    connection.setAutoCommit(true);
}

现在运行代码时会发生什么，它需要大约130米的堆空间并且需要永久运行。任何人都可以解释这种奇怪的行为吗？

Answer 1

如果第一个片段看起来很难看，我想这是一个品味问题; - ）......

然而，第二个代码片段需要更长时间（IMHO）的原因是，现在for循环的每次迭代都会创建一个新的PreparedStatement实例（getProteinIdQuery），而在第一个片段中，您重用了预准备语句，以它的方式使用它：实例化，然后提供适当的值。

至少，这是我的意见...... 扬

Answer 2

准备一份陈述需要时间，正如您所发现的那样。无论代码是否丑陋，速度的降低也非常难看，因此您需要使用更快的形式。

但你可以做的是使用内部类来保存细节并提供更好的界面：

private class DatabaseInterface {
    private PreparedStatement insertAnnotation, getProteinId;
    public DatabaseInterface() {
        // This is an inner class; 'connection' is variable in outer class
        insertAnnotation = connection.prepareStatement(
            "INSERT INTO Annotations(GOId, ProteinId, OnthologyId) VALUES(?, ?, ?)");
        getProteinId = connection.prepareStatement(
            "SELECT Id FROM Proteins WHERE PrimaryUniProtKBAccessionNumber = ?");
    }
    public long getId(Protein protein) { // Exceptions omitted...
        getProteinId.setString(1, protein.get_primary_id());
        ResultSet result = getProteinId.executeQuery();
        try {
            result.next();
            return result.getLong(1);
        } finally {
            result.close();
        }
    }
    public void insertAnnotation(int GOId, long proteinId, String ontologyId) {
        insertAnnotation.setInt(1, GOId);          // type may be wrong
        insertAnnotation.setLong(2, proteinId);
        insertAnnotation.setString(3, ontologyId); // type may be wrong
        insertAnnotation.executeUpdate();
    }
}
private void loadAnnotations(InteractionNetwork network) throws SQLException {
    connection.setAutoCommit(false);
    DatabaseInterface dbi = new DatabaseInterface();
    for(common.Protein protein : network.get_protein_vector()) {
        dbi.insertAnnotation(..., dbi.getId(protein), ...);
    }
    connection.commit();
    connection.setAutoCommit(true);
}

目标是你有一段代码知道将事情变成SQL（如果你去另一个数据库那么很容易适应）和另一段知道如何协调这些东西的代码。

在哪里用JDBC创建预准备语句？

2 个答案: