错误：并非所有代码路径都返回值？

Question

I am Getting this Error (Not All Code Paths Return A Value). I want to insert data in my database with unique key constraint. but when i added this in my code my method is giving me this error.

Here is my code

  public string Insert()
    {

        SqlConnection Conn = new SqlConnection(@"Data Source=ZARAK\SQLEXPRESS;Initial Catalog=ProjectDAL;integrated security=true");


        try
        {
            Conn.Open();
            SqlCommand cmd = new SqlCommand("Insert INTO tbl_User(Name,Email,Password) VALUES ('" + name + "','" + email + "','" + password + "')", Conn);


            int restl = cmd.ExecuteNonQuery();
            //temp = true;
            return "Record Inserted successfully!";
        }
        catch (SqlException ex)
        {
            if (ex.Number == 2627)
            {
                 return "Record Already Exists";
            }
        }
        finally
        {
            Conn.Close();
        }
    }

Answer 1

Your problem is here:

catch (SqlException ex)
{
    if (ex.Number == 2627)
    {
        return "Record Already Exists";
    }
    // **
}

If you look at the code paths of your application, each if also implicitly adds an else . In this case the else doesn't contain a return statement, hence the error.

And then there's exceptions...

Exceptions are there to handle exceptional cases. There's this implicit agreement amongst software developers that catch implies handle it appropriately .

One way to handle it is to inform the user that the record already exists (I'm guessing that's what you do). If another thing happens, it's not always productive to inform the user of the error; you might simply want to try again in a few seconds (deadlock) or do something else. Usually you handle code like that on a higher level, and let the exception ripple.

As a result, I cannot tell you what the code of ** needs to be; you need to decide that for yourself based on what you want to achieve.

For example:

catch (SqlException ex)
{
    if (ex.Number == 2627)
    {
        return "Record Already Exists"; // user needs to do something
    }

    // We don't want to handle the rest here:
    throw;
}

Answer 2

In your code The possible code paths are

1. =>Try=>finally=> Exit
2. =>catch=>ex.Number == 2627=>finally=>Exit
3. =>catch=>ex.Number != 2627=>finally=>Exit

Through your code you have handled the first two; The compiler will not know what to do if he met with the third Condition that's why it showing such error. This can be solved by treating the third code path( ex.Number != 2627 ). Now consider the following code:

catch (SqlException ex)
{
    if (ex.Number == 2627)
    {
        return "Record Already Exists";
    }
    return "Some other error occurred";
}

One more thing you have to notice is the Plain Text queries. Which will opens a wide door for SQL Injection. So i request you to use parameterized queries .

Including all these changes, the Method signature for the Insert() will be like the following:

public string Insert()
{
    // Assuming Name email and passwords are global variables
    // Or else need to get them
    string conStr = @"Data Source=ZARAK\SQLEXPRESS;Initial Catalog=ProjectDAL;integrated security=true";
    int queryResult = 0;
    try
    {
        string querySQL = "Insert INTO tbl_User(Name,Email,Password)VALUES(@name,@email,@password)";
        using (SqlConnection Conn = new SqlConnection(conStr))
        {
            using (SqlCommand cmd = new SqlCommand(querySQL, Conn))
            {
                cmd.Parameters.Add("@name", SqlDbType.VarChar).Value = Name;
                cmd.Parameters.Add("@email", SqlDbType.VarChar).Value = email;
                cmd.Parameters.Add("@password", SqlDbType.VarChar).Value = password;
               queryResult= cmd.ExecuteNonQuery();
            }
        }
        return queryResult + "Record/s Inserted successfully!";
    }
    catch (SqlException ex)
    {
        if (ex.Number == 2627)
        {
            return "Record Already Exists";
        }
        return "Some other error";
    }           
}

Answer 3

Alter your code into this to make sure that you have a return value.

public string Insert()
{
    var result = String.Empty;
    SqlConnection Conn = new SqlConnection(@"Data Source=ZARAK\SQLEXPRESS;Initial Catalog=ProjectDAL;integrated security=true");


    try
    {
        Conn.Open();
        SqlCommand cmd = new SqlCommand("Insert INTO tbl_User(Name,Email,Password) VALUES ('" + name + "','" + email + "','" + password + "')", Conn);


        int restl = cmd.ExecuteNonQuery();
        //temp = true;
        result =  "Record Inserted successfully!";
    }
    catch (SqlException ex)
    {
        if (ex.Number == 2627)
        {
             result = "Record Already Exists";
        }
        else {
            result = ex.Message; // For other exceptions
        }
    }
    finally
    {
        Conn.Close();
    }

    return result;
}

Answer 4

As the error states, you must return a string in all execution paths.

public string SomeMethod()
{
    try
    {
        //Path 1
        return "Path 1";
    }
    catch (SqlException ex)
    {
        if (...) {
             //Path 2
             return "Path 2";              
        }

       //Path 3
       //Return or rethrow.
       //return "Path 3";
       throw;
    }
    finally
    {
        //Clean Up Resources
    }
}

Answer 5

If your application throw an Exception and the Exception number is not equals to 2627, your method will not return a string value.

        try
        {
            Conn.Open();
            SqlCommand cmd = new SqlCommand("Insert INTO tbl_User(Name,Email,Password) VALUES ('" + name + "','" + email + "','" + password + "')", Conn);


            int restl = cmd.ExecuteNonQuery();
            //temp = true;
            return "Record Inserted successfully!";
        }
        catch (SqlException ex)
        {
            if (ex.Number == 2627)
            {
                return "Record Already Exists";
            }
            return "Your Text";
        }
        finally
        {
            Conn.Close();
        }
        return "Your Text";
    }

Answer 6

In additional to atlaste 's nice answer. In case of C# 6.0 in order to avoid such errors and simplify try .. catch block you can put exception filter :

  try {
    ...
  }
  catch (SqlException ex) when (ex.Number == 2627) {
    return "Record Already Exists";
  }

no if , no throw;