Question

我有一个带有构造函数和方法的DBHandler类，用于更新SQLite数据库或在其中插入新记录：

public class DBHandler
    {
        private string dbName;
        private string tableName = "table1";
        private string dbPath;

        public DBHandler (string _dbName)
        {
            dbName = _dbName;
            dbPath = Path.Combine(Directory.GetCurrentDirectory (), dbName);

            bool exists = File.Exists (dbPath);
            if (!exists) {
                Mono.Data.Sqlite.SqliteConnection.CreateFile (dbPath);
                string createQuery = "CREATE TABLE " + tableName +
                                     "(" +
                                     "word1," +
                                     "word2," +
                                     "n INT INTEGER DEFAULT 1," +
                                     "PRIMARY KEY (word1, word2)" +
                                     ");";

                using (SqliteConnection connection = new SqliteConnection (String.Format ("Data Source={0};", dbPath))) {   
                    connection.Open ();
                    using (var c = connection.CreateCommand ()) {
                        c.CommandText = createQuery;
                        c.ExecuteNonQuery ();
                    }
                }
            }
        }

        public void InputToDb (WordPair pair)
        {
            string word1 = pair.word1;
            string word2 = pair.word2;
            int n = pair.n;
            int newN = 1;

            using (SqliteConnection connection = new SqliteConnection (String.Format ("Data Source={0};", dbPath))) {
                connection.Open ();

                using (var c1 = connection.CreateCommand ()) { 
                    c1.CommandText = "SELECT n from " + tableName + " WHERE word1 = '" + word1 + "' AND word2 = '" + word2 + "';";
                    var r = c1.ExecuteReader ();
                    r.Read ();
                    if (!r.HasRows)
                        newN = 1;
                    else
                        newN = int.Parse (r ["n"].ToString ()) + 1;
                } 
            }

            using (SqliteConnection connection = new SqliteConnection (String.Format ("Data Source={0};", dbPath))) {
                connection.Open ();
                using (var c2 = connection.CreateCommand ()) { 
                    string inputQuery = "INSERT OR REPLACE INTO " + tableName + " (word1, word2, n) " +
                                        "VALUES ('" + word1 + "', " +
                                        "'" + word2 + "', " +
                                        newN.ToString () +
                                        ");";
                    c2.CommandText = inputQuery;
                    c2.ExecuteNonQuery ();
                }
            }
        }
}

这个类使用如下：

DBHandler dbh = new DBHandler ("database6.db3");
 for (int i = 0; i < buffer.Count-1; i++) {
    WordPair tempPair = new WordPair (buffer.Dequeue(), buffer.Peek(), 1);
    dbh.InputToDb (tempPair);
 }

（buffer只是一个字符串队列）

这对于几次迭代（通常是8-10次）总是正常工作，然后用＆＃34;无法打开数据库＆＃34; c2.ExecuteNonQuery ();方法中字符串InputToDb(...)中的异常。在上次使用之后，看起来某些东西（连接或命令）没有正确处理，但我不知道哪里出了问题。

Answer 1

问题如下：

应该使用此

using (var r = c1.ExecuteReader ()) {
    r.Read ();
    ...
}

而不仅仅是这个

var r = c1.ExecuteReader ());
r.Read ();
...

希望您不要成为简化教程的受害者。

单声道+ SQLite。无法打开数据库

1 个答案: