An enumerable sequence of parameters (arrays, lists, etc) is not allowed in this context in Dapper

Question

I have the following code:

static void Main(string[] args){
        string sql= "SELECT * FROM Posts WHERE 1=1 ";
        SqlParameter[] @params= SetDynamicParameter(ref sql, "Param=Value", "Param2=Value2", "ParamN=ValueN");

        IDbConnection connection = new SqlConnection(connectionString);
        IEnumerable<Posts> en = connection.Query<Posts>(sql,param:@params);

        Console.ReadKey(true);
}
 static SqlParameter[] SetDynamicParameter(ref string sql,params string[] sarr) {
        string condition = string.Empty;
        List<SqlParameter> list = new List<SqlParameter>();
        foreach (var item in sarr)
        {
            condition += " AND "+item.Split('=')[0] + "=@" + item.Split('=')[0];
            list.Add(new SqlParameter("@" + item.Split('=')[0], item.Split('=')[1]));
        }
        sql += condition;
        return list.ToArray() ;
  }

The output error:An enumerable sequence of parameters (arrays, lists, etc) is not allowed in this context.

How can it be?Is there an equivalent solution?

Answer 1

Try to use Dapper.DynamicParameters instead of SqlParameter array:

var parameters = new DynamicParameters();
parameters.Add("@ParameterName", parameterValue);

Answer 2

I know this is kind of late for you, but maybe it could help somebody else:)

You can do it like this:

public class MySqlDataAccess
{
    string _connectionString = "{your connection string}";

    public async Task<IEnumerable<CustomerDto>> GetListAsync(IList<Guid> customers)
    {
        const string query = @"
            SELECT TOP 100 Id,
                    Name
            FROM Customers
            WHERE Id IN @CustomerIdList
        ";

        using (var c = new SqlConnection(_connectionString))
        {
            return await c.QueryAsync<CustomerDto>(query, new { CustomerIdList = customers.ToArray() });
        }
    }
}

You do a WHERE Id IN @CustomerIdList then passing in an anonymous type from your array like this: new { CustomerIdList = customers.ToArray() } instead of passing the array directly.

Hope it helps!

Answer 3

If you use ExecuteNonQuery instead of Query<> , you will no longer get this exception. But another problem will arise as you use Query in Oracle.

My solution to this problem was to use a intermediary table. I was using Oracle; Oracle has a special table called "dual" which is under sys schema. This table gave me inspiration and I created another table under my user's schema.

CREATE TABLE USER_SCHEMA.DUAL2
(
  DUMMY  VARCHAR2(1000 BYTE)
)
NOCOMPRESS 
NOCACHE
NOPARALLEL;

You can extend length if you wish. Gave some grants to table. Then I changed my query from select to insertion for select statement.

INSERT INTO USER_SCHEMA.DUAL2
   (SELECT ID
      FROM ANOTHER_SCHEMA.SOME_TABLE
     WHERE SOME_FLAG = 'M' AND NO IN :NO)

This is because ADO.NET is not able to return a result from ExecuteNonQuery . By default it runs SELECT queries but returns -1 for each query. I am simulating an INSERT by providing a SELECT query. This returns a result.

var parameters = noSplit.Select(x => new { NO = x, SOME_FLAG = flag }).ToList();

var queryResult = dbConnection.Execute(insertSelectQuery, parameters, transactionIfExists);

if (queryResult != parameters.Count)
{
    throw new Exception("Can not find some no");
}

Answer 4

Dapper will take an IEnumerable as the param argument and insert multiple records. This is what I was passing, so I was confused when I got the error message above.

My mistake was that I copied and pasted from another method that was calling connection.Query instead of connection.Execute .

So, if your query is already specifying the columns, also check that you're calling Execute and not some other method.