How to map to a Dictionary object from database results using Dapper Dot Net?

There's various ways already shown; personally I'd just use the non-generic api:

var dict = conn.Query(sql, args).ToDictionary(
    row => (string)row.UniqueString,
    row => (int)row.Id);

string strSql = "SELECT DISTINCT TableID AS [Key],TableName AS [Value] FROM dbo.TS_TStuctMaster";
Dictionary<string,string> dicts = sqlConnection.Query<KeyValuePair<string,string>>(strSql).ToDictionary(pair => pair.Key, pair => pair.Value);

You can use aliases and strong types.

Aliases are the key points, which match the attributes of KeyValuePair type Key and Value.

It works under strong typing and runs well.

I don't like dynamic type. It brings disaster in certain situations. Moreover, the boxing and unboxing brings performance loss.

Works also without an additional class:

var myDictionary = conn.Query<string, int, KeyValuePair<string,int>>(sql, (s,i) => new KeyValuePair<string, int>(s,i))
    .ToDictionary(kv => kv.Key, kv => kv.Value);

NOTE: When using Dapper.NET 3.5 version, the Query method that takes the first, second and return types requires you specify more parameters, as the .NET 4.0 and .NET 4.5 versions take advantage of optional arguments.

In this case, the following code should work:

string splitOn = "TheNameOfTheValueColumn";
var myDictionary = conn.Query<string, int, KeyValuePair<string,int>>(sql, (s,i) => new KeyValuePair<string, int>(s,i), null, null, false, splitOn, null, null)
        .ToDictionary(kv => kv.Key, kv => kv.Value);

Most of the arguments will revert to a default, but splitOn is required, as it will otherwise default to a value of 'id'.

For a query that returns two columns, 'ID' and 'Description', splitOn should be set to 'Description'.

If you are using > .net 4.7 or netstandard2 you can use value tuples. the code is nice and terse and there is no use of dynamics.

var sql = "SELECT UniqueString, Id  FROM Table";
var dict = conn.Query<(string UniqueString, int Id)>(sql)
           .ToDictionary(t => t.UniqueString,t => t.Id);