Daily Knowledge Drop
.NET 7 introduces the ability to automatically bind a query string value to an array (or StringValues class).
When the query string value is of variable length and can contain one or more different items - this automatic binding can save time and facilitates cleaner code.
Pre .NET7
Prior to .NET 7, a query string parameter with multiple values would manually need to be converted to an array:
app.MapGet("/getsongs", async ([FromQuery] string artists) =>
{
async IAsyncEnumerable<string> GetSongs(string[] artists)
{
foreach (var name in artists)
{
/// simulate looking up all the
// songs for the artist
yield return $"Retrieving songs for '{name}'";
}
}
// the artist parameter value would be
// comma separated of all the values supplied
return GetSongs(artists.Split(","));
});
Calling the endpoint with /getsongs?artists=foofighters&artists=johnmayer, will result in the artists parameter having a value of foofighters,johnmayer (all values supplied in a comma separated string). The return value:
["Retrieving songs for 'foofighters'","Retrieving songs for 'johnmayer'"]
.NET7
Array binding
Leveraging this new array binding functionality is very simple:
// Automatically bind the query string value "artists" to the
// endpoint array parameter "artists"
app.MapGet("/getsongs", async ([FromQuery] string[] artists) =>
{
// create a local function to be able to yield return
// from the endpoint
async IAsyncEnumerable<string> GetSongs(string[] artists)
{
foreach (var name in artists)
{
/// simulate looking up all the
// songs for the artist
yield return $"Retrieving songs for '{name}'";
}
}
// no conversion required
return GetSongs(artists);
});
Calling the endpoint with a single value, by browsing to the endpoint /getsongs?artists=foofighters, gives the following result:
["Retrieving songs for 'foofighters'"]
While calling the endpoint with multiple values, /getsongs?artists=foofighters&artists=johnmayer, results in:
["Retrieving songs for 'foofighters'","Retrieving songs for 'johnmayer'"]
StringValues binding
The query string parameter can also be bound to a StringValues instance if required. This operates the same as the array:
// Automatically bind the query string value "artists" to the
// endpoint StringValues parameter "artists"
app.MapGet("/getsongs", async ([FromQuery] StringValues[] artists) =>
{
// create a local function to be able to yield return
// from the endpoint
async IAsyncEnumerable<string> GetSongs(StringValues artists)
{
foreach (var name in artists)
{
/// simulate looking up all the
// songs for the artist
yield return $"Retrieving songs for '{name}'";
}
}
return GetSongs(artists);
});
Notes
This approach is significantly simpler and cleaner than having to split the query string into an array manually. While this enhancement will not drastically change the performance of an application or add significant new functionality, it does facilitate cleaner, more readable code, which day to day, is probably more important for the vast majority of application.
References
.NET 7: Microsoft Reveals New ASP.NET Core Features
Daily Drop 185: 19-10-2022
At the start of 2022 I set myself the goal of learning one new coding related piece of knowledge a day.
It could be anything - some.NET / C# functionality I wasn't aware of, a design practice, a cool new coding technique, or just something I find interesting. It could be something I knew at one point but had forgotten, or something completely new, which I may or may never actually use.
The Daily Drop is a record of these pieces of knowledge - writing about and summarizing them helps re-enforce the information for myself, as well as potentially helps others learn something new as well.