Setting OData result Page Size at runtime in WebAPI app - asp.net

Question

I am writing an ASP.NET Web API 2 web service using OdataControllers I have found out how to set page size using the PageSize Property of the EnableQueryAttribute. I want to allow the users of my web service to set the page size in the app.config and then have the application read this setting and set the page size. The problem is that using the attribute requires Page Size be set to a compile time constant.
Usage of attribute:
[EnableQuery(PageSize = 10)]
public IHttpActionResult GetProducts()
{
return repo.GetProducts();
}
One proposed solution I have seen is to construct the EnableQueryAttribute and set it on the HTTPConfiguration config object like this
int customSize = ReadPageSizeSettingFromConfigFile();
var attr = new EnableQueryAttribute { PageSize = customSize };
config.AddODataQueryFilter(attr);
but this doesn't actually work. The HttpConfiguration's Filter collection remains empty.
A comment on another post (buried in a list of comments) suggested removing all the EnableQuery attributes on the controllers but that has no effect either. Since the EnableQuery attribute replaced the older Queryable attribute I am wondering if this is a Microsoft problem.
This question has been asked and not answered before: How limit OData results in a WebAPI
All help is greatly appreciated.

Answer 1

You can use $top and $skip to achieve your goal, if client want pagesize is 10, and want the second page:
localhost/odata/Customers?$top=10&$skip=10
About dynamically set the pagesize:
public class MyEnableQueryAttribute : EnableQueryAttribute
{
public override IQueryable ApplyQuery(IQueryable queryable, ODataQueryOptions queryOptions)
{
int pagesize = xxx;
var result = queryOptions.ApplyTo(queryable, new ODataQuerySettings { PageSize = pagesize });
return result;
}
}
and put this attribute in your controller method.

Answer 2

You can set config for MaxTop in webApiConfig resgister method
public static class WebApiConfig{
public static void Register(HttpConfiguration config){
config.Select().Expand().Filter().OrderBy().MaxTop(100).count() // you can change max page size here
}
}

Answer 3

I was able to accomplish this by creating a new attribute (I called it ConfigurableEnableQueryAttribute) that extends the enable query attribute. In the constructor for that attribute, load your config file and set any settings you are interested in in the base. Personally I loop through all settings provided in an "OData" section of my appsettings, and if there are matching settings in the EnableQuery attribute, I cast them to the specified type and supply them, but you can only look for specific settings if you want.
My attribute:
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public class ConfigurableEnableQueryAttribute : EnableQueryAttribute
{
public ConfigurableEnableQueryAttribute()
{
var builder = new ConfigurationBuilder().AddJsonFile("appsettings.json");
var configuration = builder.Build();
var configProps = configuration.GetSection("OData").GetChildren();
var baseProps = typeof(EnableQueryAttribute).GetProperties();
foreach (var configProp in configProps)
{
var baseProp = baseProps.FirstOrDefault(x => x.Name.Equals(configProp.Key));
if (baseProp != null)
{
baseProp.SetValue(this, Convert.ChangeType(configProp.Value, baseProp.PropertyType));
}
}
}
}
and then in the controller
[HttpGet]
[ConfigurableEnableQuery]
public IQueryable<T> Get()
{
return _context.Set<T>().AsQueryable();
}