无法将“DapperRow”类型的对象转换为“System.String”类型

Question

I'm using Dapper to access database objects.

So this line

Console.Write(string.Join(System.Environment.NewLine, results));

Gives me

{DapperRow, VALUE_A = 'Y', VALUE_B = 'Y'}

But i'd like to access or print these values like

DapperRow, 
VALUE_A = 'Y'
VALUE_B = 'Y'

But I am getting "System.InvalidCastException: Unable to cast object of type 'DapperRow' to type 'System.String'" with the following code. Where i am trying to use foreach to loop through this list.

using (var conn = new OracleConnection("Password=xxxxx;Persist Security Info=True;User ID=xxxxx;Data Source=xxxxx"))
{
// dapper adds an extension method to the connection for querying
string sql = "SELECT X, Y FROM Z WHERE ABC = 123";
var results = conn.Query(sql).ToList();
Console.Write(string.Join(System.Environment.NewLine, results));

    foreach (string value in results)
    {
    Console.WriteLine("> {0}",value);
    }
}

Answer 1

Actually this gives me the result i want..

using (var conn = new OracleConnection("Password=xxxxx;Persist Security Info=True;User ID=xxxxxxx;Data Source=xxxxxx"))
{
string sql = "SELECT X, Y FROM Z WHERE ABC = 123";
var orderDetail = conn.Query(sql).FirstOrDefault();

    foreach (var pair in orderDetail)
    {
        Console.WriteLine("{0} = {1}", pair.Key, pair.Value);
    }
}

Output: 
VALUE_A = 'Y'
VALUE_B = 'Y'

Then with something like this i can get a value of 'Y' returned.

if (pair.Key == "VALUE_B")
{
Console.WriteLine("Val {0}", pair.Value);
}

Answer 2

Citing the manual as reference:

string sql = "SELECT * FROM Invoice WHERE InvoiceID = @InvoiceID; SELECT * FROM InvoiceItem WHERE InvoiceID = @InvoiceID;";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    using (var multi = connection.QueryMultiple(sql, new {InvoiceID = 1}))
    {
        var invoice = multi.Read<Invoice>().First();
        var invoiceItems = multi.Read<InvoiceItem>().ToList();
    }
}

would mean that your code would change to something like

        string sql = "SELECT X, Y FROM Z WHERE ABC = @ABC";
        using (var conn = new OracleConnection("Password=xxxxx;Persist Security Info=True;User ID=xxxxx;Data Source=xxxxx"))
        using (var multi = conn.QueryMultiple(sql, new {ABC = 123}))
        {
            var results = multi.Read<Z>().ToList();
            Console.Write(string.Join(System.Environment.NewLine, results.Count));
            foreach (string value in results)
            {
                Console.WriteLine("> X:{0} Y:{1}",value.X, value.Y);
            }
        }

Answer 3

This is late but I just solved a similar issue I was facing and thought to share. With Dapper, you can transform object into the needed type on Query. So write a class with the properties X, Y

class DataReturned
{
public string X {get; set;}
public string Y {get; set;}
}

Then when querying you do this

var results = conn.Query<DataReturned>(sql).ToList();

instead of this

var results = conn.Query(sql).ToList();

This will remove the DapperRow and give you just the list you can use. You may not need the class if you only want one value which you cast to a primitive type

var results = conn.Query<string>(sql).ToList();

Am sure you can even cast to string array, dictionary or any other type, just have not experimented that.