$count is evaluated prematurely at the call queryOptions.ApplyTo

[congysu]

internal static class ExpressionHelpers
{
    public static long Count(IQueryable query, Type type)
    {
        MethodInfo countMethod = ExpressionHelperMethods.QueryableCountGeneric.MakeGenericMethod(type);
        return (long)countMethod.Invoke(null, new object[] { query });
    }

A query
http://localhost:31181/api/northwind/Products?$count=true
will evaluate the query expression prematurely at the call
queryable = queryOptions.ApplyTo(queryable, settings);

This breaks RESTier, specifically, in DomainControllers.GetQuery method.
Since at that time QuerySourcer has not intervened in, the placeholder class QueryableSource will be queried against, and exception will be thrown.

Call stack:

System.Web.OData.dll!System.Web.OData.ExpressionHelpers.Count(System.Linq.IQueryable query, System.Type type) Line 18 C#
System.Web.OData.dll!System.Web.OData.Query.CountQueryOption.GetEntityCount(System.Linq.IQueryable query) Line 138 C#
System.Web.OData.dll!System.Web.OData.Query.ODataQueryOptions.ApplyTo(System.Linq.IQueryable query, System.Web.OData.Query.ODataQuerySettings querySettings) Line 239 C#

[congysu]

Checked in 5332139.

[lewischeng-ms]

RESTier can call ODataQueryOptions.ApplyTo with ignoreQueryOptions set to AllowedQueryOptions.Count to work around this issue. And then later set the TotalCount to QueryResult in QueryExecutor.

[VikingsFan]

Merged 337a8cc