Dapper Order By | 易学教程

问题

Is there any reason why the following code wouldn't be retrieved in the correct order when using dapper?

connection.Query<User>("SELECT id, name " +
                       "FROM user " +
                       "ORDER BY @sort @dir " +
                       "LIMIT @offset, @pageSize; ",
                       new {
                           sort = sortOrder, // sortOrder = "name"
                           dir = sortDirection, // sortDirection = "ASC"
                           offset = pageIndex * pageSize, // offset = 0
                           pageSize = pageSize // pageSize = 10
                       });

It always returns without applying the ordering.

I could just place the sortOrder and sortDirection directly into the string like this

"SELECT id, name " +
"FROM user " +
"ORDER BY " + sortOrder + " " + sortDirection + " " +
"LIMIT @offset, @pageSize; "

but I'm not sure how that will effect dapper since I believe it has it's own query plan caching.

Also, is there a way to view the query that is generated by dapper?

回答1:

Sure, in general database engines do not allow you to parametrize column names. So for example:

var row = cnn.Query("select @bob as col from table", new {bob = "col"}).first(); 
// most likely returns "row.col == col"

When you are trying to parametrize order by clauses I would recommend using inline substitution, provided you can guarantee your escaping, bobby tables is always lurking. (Either that or you could use a proc)

I am not sure about the situation around profilers for (MySQL? Oracle?) but you could use a tool like MiniProfiler to see the SQL.

It will affect caching, however there are only a small number of permutations of sortOrder and sortDirection so the impact is minimal.

回答2:

You can just use a case statement in your order by. As long as you're only dealing with a few columns, it won't get too crazy.

public List<Signup> GetNext(int Id, int RowsToFetch, string SortedBy)
        {

            string _sortedBy = SortedBy.Trim();
            using (IDbConnection conn = Connection)
            {
                string sQuery = @"SELECT TOP(@ROWSTOFETCH)
                                    [Id]
                                   ,[FirstName]
                                   ,[LastName]
                                   ,[EmailAddress]
                                  FROM [dbo].[vwBaseQuery]
                                  WHERE ID >= @ID
                                  ORDER BY 
                                          CASE WHEN @SORTEDBY = 'Id ASC' THEN Id END ASC,
                                          CASE WHEN @SORTEDBY = 'Id DESC' THEN Id END DESC,
                                          CASE WHEN @SORTEDBY = 'FirstName ASC' THEN FirstName END ASC,
                                          CASE WHEN @SORTEDBY = 'FirstName DESC' THEN FirstName END DESC,
                                          CASE WHEN @SORTEDBY = 'LastName ASC' THEN LastName END ASC,
                                          CASE WHEN @SORTEDBY = 'LastName DESC' THEN LastName END DESC,
                                          CASE WHEN @SORTEDBY = 'EmailAddress ASC' THEN EmailAddress END ASC,
                                          CASE WHEN @SORTEDBY = 'EmailAddress DESC' THEN EmailAddress END DESC";
                conn.Open();

                var result = conn.Query<Signup>(sQuery, new {
                    SORTEDBY = _sortedBy,
                    ROWSTOFETCH = RowsToFetch,
                    ID = Id
                }).ToList();
                return result;
            }
        }

来源：https://stackoverflow.com/questions/9344340/dapper-order-by

标签

sql-order-by

dapper