c# - 在没有 Entity Framework 的情况下使用 C# 进行数据库交互

Question

我接到了一项任务，我需要显示一个表单，该表单的数据驻留在 Sql server 的各种表中。要求严格不要使用 Entity Framework 或存储过程。在这种情况下，我有什么选择？

目前我正在使用 SqlCommand 对象运行一些 sql 查询，但是当涉及到获取关系数据然后允许用户从表单更新它时，事情变得非常复杂。

Winforms 中允许查看和编辑关系数据的最佳方法是什么？

Answer 1

您可以为需要访问/更新的对象编写自己的简单类。 出于以下示例的目的，我们假设您有 2 个表:

人

• Person_Id INT PRIMARY KEY NOT NULL
• 名称 NVARCHAR(100) NULL

电子邮件

• Person_Id INT PRIMARY KEY NOT NULL
• Email_Id INT PRIMARY KEY NOT NULL

• 电子邮件 NVARCHAR(100) NOT NULL

  public class MyProgram
  {
  
      public List<Person> ReadRecords()
      {
          // Set up your connection
          SqlConnection conn = new SqlConnection();
          conn.Open();
  
          SqlCommand cmd = new SqlCommand("SELECT * FROM Person", conn);
          SqlDataReader reader = cmd.ExecuteReader();
  
          List<Person> personRecords = new List<Person>();
  
          while (reader.Read())
          {
              Person p = new Person(reader, conn);
              personRecords.Add(p);
          }
  
          return personRecords;
      }
  
      public int UpdateRecords(IEnumerable<Person> records, SqlConnection conn)
      {
          int personsUpdated = 0;
          int recordsUpdated = 0;
  
          foreach (Person p in records)
          {
              if (p.Changed)
              {
                  recordsUpdated += p.Update(conn);
                  personsUpdated++;
              }
          }
  
          return recordsUpdated;
      }
  }
  
  public class Person
  {
      public const string SqlGetPersonEmailsCommand = "SELECT Email_Id, Email FROM Emails WHERE Person_Id = @Person_Id";
      public const string SqlUpdatePersonCommand = "UPDATE Person SET Name = @Name WHERE Id = @OriginalId";
      public const string SqlUpdatePersonEmailCommand = "UPDATE Emails SET Email = @Email WHERE Email_Id = @Email_Id";
  
      public int OriginalId { get; private set; }
  
      private bool personChanged;
      private bool emailsChanged { get { return changedEmails.Count > 0; } }
      public bool Changed { get { return personChanged || emailsChanged; } }
  
      private int _id;
      public int Id
      {
          get { return _id; }
          set
          {
              throw new Exception("Changing Id is not allowed.");
          }
      }
  
      private string _name;
  
      public string Name
      {
          get { return _name; }
          set
          {
              _name = value;
              personChanged = true;
          }
      }
  
      private List<int> changedEmails;
      private Dictionary<int, string> _emailAddresses;
      public string[] EmailAddresses
      {
          get
          {
              string[] values = new string[_emailAddresses.Count];
              _emailAddresses.Values.CopyTo(values, 0);
              return values;
          }
      }
  
      public void UpdateEmail(int emailId, string newEmail)
      {
          _emailAddresses[emailId] = newEmail;
          changedEmails.Add(emailId);
      }
  
      public Person(IDataReader reader, SqlConnection conn)
      {
          // Read ID (primary key from column 0)
          OriginalId = _id = reader.GetInt32(0);
  
          // Check if value in column 1 is Null; if so, set _name to Null, otherwise read the value
          _name = reader.IsDBNull(1) ? null : reader.GetString(1);
  
          // Now get all emails for this Person record
          SqlCommand readEmailsCmd = new SqlCommand(SqlGetPersonEmailsCommand, conn);
          readEmailsCmd.Parameters.Add("@Person_Id", SqlDbType.Int);
          readEmailsCmd.Parameters["@Person_Id"].Value = OriginalId;
  
          SqlDataReader emailReader = readEmailsCmd.ExecuteReader();
  
          changedEmails = new List<int>();
          _emailAddresses = new Dictionary<int, string>();
  
          if (emailReader.HasRows)
          {
              while (emailReader.Read())
              {
                  int emailId = emailReader.GetInt32(0);
                  string email = emailReader.GetString(1);
  
                  _emailAddresses.Add(emailId, email);
              }
          }
      }
  
  
      public int Update(SqlConnection conn)
      {
          int rowsUpdated = 0;
  
          SqlCommand command = null;
  
          // Update Person record
          if (personChanged)
          {
              command = new SqlCommand(SqlUpdatePersonCommand, conn);
  
              command.Parameters.Add("@OriginalId", SqlDbType.Int);
              command.Parameters["@OriginalId"].Value = OriginalId;
  
              command.Parameters.Add("@Name", SqlDbType.NVarChar);
              command.Parameters["@Name"].Value = _name;
  
              rowsUpdated = command.ExecuteNonQuery();
          }
  
          // Now update all related Email records
          foreach (int id in changedEmails)
          {
              command = new SqlCommand(SqlUpdatePersonEmailCommand, conn);
  
              command.Parameters.Add("@Email_Id", SqlDbType.Int);
              command.Parameters["@Email_Id"].Value = id;
  
              command.Parameters.Add("@Email", SqlDbType.NVarChar);
              command.Parameters["@Email"].Value = _emailAddresses[id];
  
              rowsUpdated = +command.ExecuteNonQuery();
          }
  
          return rowsUpdated;
      }
  }
  

以上示例支持更改人员的姓名和关联的电子邮件地址。