Question

此代码无效。任何人都可以指导我在哪里可以找到使用C＃动态创建Postgresql数据库和表的示例？

     const string connStr = "Server=localhost;Port=5432;
                          User Id=postgres;Password=enter;Database=postgres";

        var m_conn = new NpgsqlConnection(connStr);

        // creating a database in Postgresql
        m_createdb_cmd = new NpgsqlCommand("CREATE DATABASE IF NOT EXISTS  \"testDb\" " +
                                       "WITH OWNER = \"postgres\" " +
                                       "ENCODING = 'UTF8' " +
                                       "CONNECTION LIMIT = -1;", m_conn);

        // creating a table in Postgresql
        m_createtbl_cmd = new NpgsqlCommand(
            "CREATE TABLE MyTable(CompanyName VARCHAR(150))";

        m_conn.Open();
        m_createdb_cmd.ExecuteNonQuery();
        m_createtbl_cmd.Connection = m_conn;
        m_conn.Close();

已创建数据库，但在创建表时出现静默失败。

Answer 1

我会这样做：

string connStr = "Server=localhost;Port=5432;User Id=postgres;Password=enter;";
var m_conn = new NpgsqlConnection(connStr);
var m_createdb_cmd = new NpgsqlCommand(@"
    CREATE DATABASE IF NOT EXISTS testDb
    WITH OWNER = postgres
    ENCODING = 'UTF8'
    CONNECTION LIMIT = -1;
    ", m_conn);
m_conn.Open();
m_createdb_cmd.ExecuteNonQuery();
m_conn.Close();

connStr = "Server=localhost;Port=5432;User Id=postgres;Password=enter;Database=testDb";
m_conn = new NpgsqlConnection(connStr);
m_createtbl_cmd = new NpgsqlCommand(
   "CREATE TABLE table1(ID CHAR(256) CONSTRAINT id PRIMARY KEY, Title CHAR)"
   , m_conn);
m_conn.Open();
m_createtbl_cmd.ExecuteNonQuery();
m_conn.Close();

不建议在此处使用var。我使用它，因为我不知道返回的类型是什么，但你应该。

请注意使用原始字符串（@）。它使字符串构建变得简单。

除非标识符是非法的，否则不要在Postgresql中使用双引号括起来的标识符。它会让你的生活更加艰难。

Answer 2

您似乎忘记调用ExecuteNonQuery

的m_createtbl_cmd:方法

m_createtbl_cmd.ExecuteNonQuery();

您也可以使用DynORM库简化它：http://dynorm.codeplex.com/

希望它有所帮助！

Answer 3

<强>解决方案：

    // 1. Connect to server to create database:
    const string connStr = "Server=localhost;Port=5432;User Id=postgres;Password=enter;";

    // 2. Connect to server to create table:
    const string connStr2 = "Server=localhost;Port=5432;User Id=postgres;Password=enter;Database=testDb";


    var m_conn = new NpgsqlConnection(connStr); // db connction
    var m_conn2 = new NpgsqlConnection(connStr2); // table connection

    // creating a database in Postgresql
    m_createdb_cmd = new NpgsqlCommand("CREATE DATABASE IF NOT EXISTS  \"testDb\" " +
                                   "WITH OWNER = \"postgres\" " +
                                   "ENCODING = 'UTF8' " +
                                   "CONNECTION LIMIT = -1;", m_conn);

    // creating a table in Postgresql
    m_createtbl_cmd = new NpgsqlCommand
       {
       CommandText ="CREATE TABLE table1(ID CHAR(256) CONSTRAINT id PRIMARY KEY, Title CHAR)"
       };

       m_createtbl_cmd.Connection = m_conn2;

 // 3.. Make connection and create

        // open connection to create DB
        m_conn.Open();
        m_createdb_cmd.ExecuteNonQuery();
        m_conn.Close();

        // open connection to create table
        m_conn2.Open();
        m_createtbl_cmd.ExecuteNonQuery();
        m_conn2.Close();

这样可行，但有更短的方法吗？我不得不创建两个Npgsql连接。我不知道，对我来说看起来并不优雅。

Answer 4

这对我来说用C＃验证任何Postgres数据库是否有用：

private bool chkDBExists(string connectionStr, string dbname)
{
    using (NpgsqlConnection conn = new NpgsqlConnection(connectionStr))
    {
        using (NpgsqlCommand command = new NpgsqlCommand
            ($"SELECT DATNAME FROM pg_catalog.pg_database WHERE DATNAME = '{dbname}'", conn))
        {
            try
            {
                conn.Open();
                var i = command.ExecuteScalar();
                conn.Close();
                if (i.ToString().Equals(dbname)) //always 'true' (if it exists) or 'null' (if it doesn't)
                    return true;
                else return false;
            }
            catch (Exception e) { return false; }
        }
    }
}

** try-catch语句中使用的if可以简单地检查ExecuteScalar的返回值对于不存在的DB是否为null，如果存在则不为null。

Postgresql - 创建数据库＆amp;表动态

4 个答案: