How to create arguments for a Dapper query dynamically

I know this is an old question (like, 5 years old) but I was struggling with the same thing. The complete answer is in the comments to the other answer, but I thought I would offer a full example here.

string query = "SELECT * FROM MyTableName WHERE Foo = @Foo AND Bar = @Bar";

Dictionary<string, object> dictionary = new Dictionary<string, object>();
dictionary.Add("@Foo", "foo");
dictionary.Add("@Bar", "bar");

var results = connection.Query<MyTableName>(query, new DynamicParameters(dictionary));

Or, to be fully dynamic, you can create a method like this, which will take any model, any query, and any set of query parameters:

public static IEnumerable<T> Get<T>(string query, Dictionary<string, object> dictionary)
{
    IEnumerable<T> entities = connection.Query<T>(query, new DynamicParameters(dictionary));
    return entities;
}

And then to call this method:

var results = Get<MyTable>(query, dictionary)

EDIT LONG AFTER

This answer continues to get upvotes, so this is apparently still a need. I took this solution and created an entire data access NuGet package built on top of Dapper. It reduces your CRUD and query operations to a single line of code.

Here's the NuGet package.

One can also use an ExpandoObject as the parameters of a query, instead of the Dapper-specific class DynamicParameters:

ExpandoObject param = new ExpandoObject();

IDictionary<string, object> paramAsDict = param as IDictionary<string, object>;
paramAsDict.Add("foo", 42);
paramAsDict.Add("bar", "test");

MyRecord stuff = connection.Query<MyRecord>(query, param);

Yes:

var dbArgs = new DynamicParameters();
foreach(var pair in args) dbArgs.Add(pair.Key, pair.Value);

Then pass dbArgs in place of args:

var stuff = connection.Query<ExtractionRecord>(query, dbArgs);

Alternatively, you can write your own class that implements IDynamicParameters.

Note that if you are starting from an object (the usual approach with dapper), you can also use this template with DynamicParameters as a starting point:

var dbArgs = new DynamicParameters(templateObject);