C#中如何检查表是否存在

Question

首先，让我告诉你我检查了一堆“如何检查......中是否存在表”。不过，我需要有关查询的更多信息

\n\n

SELECT name FROM sqlite_master WHERE type=\'table\' AND name=\'table_name\';\n

\n\n

我想我必须更改名称“sqlite_master”和“table_name”，这是我的代码

\n\n

// a static function of the public class "SqliteBase"\npublic static void CreerBase(string dataSource)\n{\n    SQLiteConnection connection = new SQLiteConnection();\n\n    connection.ConnectionString = "Data Source=" + dataSource;\n    connection.Open();\n    SQLiteCommand command = new SQLiteCommand(connection);\n\n    // Create table if it does not exist\n    command.CommandText = "CREATE TABLE IF NOT EXISTS beispiel ( id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, name VARCHAR(100) NOT NULL);";\n    Console.WriteLine("La Table a bien \xc3\xa9t\xc3\xa9 cr\xc3\xa9\xc3\xa9e");\n    command.ExecuteNonQuery();\n    command.Dispose();\n    connection.Close();\n    connection.Dispose();\n}\n

\n\n

和单元测试功能：

\n\n

[TestMethod]  \npublic void LaCreationBaseMarche()\n{\n    string dataSource = "beispiel.db";\n    SqliteBase.CreerBase(dataSource);\n    SQLiteConnection connection = new SQLiteConnection();\n\n    connection.ConnectionString = "Data Source=" + dataSource;\n    connection.Open();\n    SQLiteCommand command = new SQLiteCommand(connection);\n    command.CommandText = "SELECT name FROM sqlite_master WHERE type = \'table\' AND name = \'beispiel\';";\n    SQLiteDataReader reader = command.ExecuteReader();\n    Assert.Equals("beispiel", reader[0].ToString());\n    reader.Close();\n    reader.Dispose();\n\n    command.Dispose();\n\n}\n

\n\n

我的问题是：command.executeReader()测试方法的返回给我一个“null”阅读器，当然，当我尝试执行 reader[0] 时，我收到了错误。我是否误用了查询？

\n\n

编辑：好的，我虽然必须使用文件名^^。现在我改变了它，但它仍然不起作用（同样的错误）。我还更改了“beispiel.db”中的名称“exemple.db”。我更新了我的代码:)

\n\n

预先感谢您的回答:)

\n

Answer 1

不，您不必更改sqlite_master. 这是 SQLite 的元数据表，其中包含有关 SQLite 已知的所有对象的信息。

所以你的查询将变成：

SELECT name FROM sqlite_master WHERE type='table' AND name='beispiel';

Answer 2

我执行了以下操作来检查数据库中是否已存在表

public static bool tableAlreadyExists(SqliteConnection openConnection, string tableName)
{
  var sql = 
  "SELECT name FROM sqlite_master WHERE type='table' AND name='"+tableName +"';"; 
  if(openConnection.State == System.Data.ConnectionState.Open)
  {   
        SqliteCommand command = new SqliteCommand(sql, openConnection);
        SqliteDataReader reader =command.ExecuteReader();
        if(reader.HasRows)
        {
            reader.Close(); // @al000y: thanks mate
            return true;
        }
        reader.Close(); // @al000y: thanks mate
        return false;
    }else{
        throw new System.ArgumentException("Data.ConnectionState must be open");
    }
}