SqlQuerySpec parameterized query returns no results - azure-cosmosdb

Question

I'm not sure whether it is an emulator issue or not but i have a really simple query
var collectionUri = UriFactory.CreateDocumentCollectionUri(Constants.CosmosDbName, CollectionName);
var spec = new SqlQuerySpec()
{
QueryText = "SELECT * FROM Users u WHERE u.firstName = #firstname",
Parameters = new SqlParameterCollection
{
new SqlParameter{
Name = "#firstname",
Value = value
}
}
};
var query = client.CreateDocumentQuery<User>(collectionUri, spec);
var users = await query.ToListAsync();
the parametrized query returns no results i.e. 0 users
while the same plain query below retuns 1 user that matches the WHERE condition:
spec.Parameters.Clear();
spec.QueryText = $"SELECT * FROM Users u WHERE u.firstName = '{value}'";
query = client.CreateDocumentQuery<User>(collectionUri, spec);
users = await query.ToListAsync(); // returns 1 user
do I need somehow explicitly enable parameterized queries
or am I doing something wrong above with a parameterized query?

Answer 1

According to the Syntax, your query should be like this,
SqlQuerySpec sqlQuerySpec = new SqlQuerySpec
{
QueryText = #"SELECT *
FROM Users u
WHERE u.u.firstName = #firstname",
Parameters = new SqlParameterCollection
{
new SqlParameter("#firstname", value)
}
};

Answer 2

The issue is a kind of var pitfall
the SqlParameter value was taken from an Azure function HttpRequest request:
var value = req.Query["firstname"];
which is
Microsoft.Extensions.Primitives.StringValues value = req.Query["firstname"];
When SqlParameter is created with value of StringValues type it makes slightly different query:
SELECT * FROM Users u WHERE u.firstName = ['Dima']
the brackets ['Dima'] here are excess
the correct query must be without brackets
SELECT * FROM Users u WHERE u.firstName = 'Dima'
so to fix the parameterized query the parameter value should be a string
new SqlParameter("#firstname",value.ToString())