Paging

When a static query method on a [ReadModel] returns IQueryable<T>, the query pipeline automatically applies server-side paging and sorting. You write a simple method that returns a queryable, and the framework handles the rest.

Why IQueryable matters

The key to automatic paging is returning IQueryable<T> instead of IEnumerable<T> or List<T>. When the pipeline sees an IQueryable, it appends .Skip() and .Take() before the database executes the query — so only the requested page of data travels over the wire.

If you return a materialized collection, all rows are fetched first and paging cannot be applied at the database level.

[ReadModel]
public record DebitAccount(AccountId Id, AccountName Name, CustomerId Owner, decimal Balance)
{
    // ✅ Returns IQueryable — paging and sorting are applied automatically
    public static IQueryable<DebitAccount> AllAccounts(IMongoCollection<DebitAccount> collection)
        => collection.AsQueryable();
}

How it works

When a client sends paging parameters in the query string, the QueryableQueryRenderer intercepts the IQueryable result and:

1. Counts the total number of matching items
2. Applies sorting based on sortby and sortDirection
3. Applies .Skip(page * pageSize) and .Take(pageSize)
4. Returns the page of data wrapped in a QueryResult with a PagingInfo containing page, size, totalItems, and totalPages

The client controls paging with these query string parameters:

Parameter	Type	Description
page	int	Zero-based page number
pageSize	int	Number of items per page
sortby	string	Field name to sort by
sortDirection	asc or desc	Sort direction

Example requests

GET /api/debitaccount/allaccounts?page=0&pageSize=25
GET /api/debitaccount/allaccounts?page=1&pageSize=10&sortby=name&sortDirection=asc

When no paging parameters are provided, the full result set is returned without paging.

Complete example with filtering

Paging works alongside query arguments. The pipeline applies paging after your method returns the filtered IQueryable:

[ReadModel]
public record DebitAccount(AccountId Id, AccountName Name, CustomerId Owner, decimal Balance)
{
    public static IQueryable<DebitAccount> AllAccounts(IMongoCollection<DebitAccount> collection)
        => collection.AsQueryable();

    public static IQueryable<DebitAccount> AccountsByOwner(
        CustomerId ownerId,
        IMongoCollection<DebitAccount> collection)
        => collection.AsQueryable().Where(a => a.Owner == ownerId);
}

Both query methods support paging automatically because they return IQueryable<T>.

Return type comparison

Return type	Paging	Sorting	DB-level optimization
IQueryable<T>	✅ Automatic	✅ Automatic	✅ Skip/Take pushed to DB
IEnumerable<T>	❌	❌	❌ All rows loaded
List<T>	❌	❌	❌ All rows loaded
T[]	❌	❌	❌ All rows loaded

Observable queries with paging

Observable queries that return ISubject<IEnumerable<T>> also support automatic paging. The pipeline applies paging to each update pushed through the observable:

[ReadModel]
public record DebitAccount(AccountId Id, AccountName Name, CustomerId Owner, decimal Balance)
{
    public static ISubject<IEnumerable<DebitAccount>> ObserveAllAccounts(
        IMongoCollection<DebitAccount> collection)
        => collection.Observe();
}

Frontend integration

The generated TypeScript proxy includes a useWithPaging method when the backend query supports paging. See React Paging for details on using paging in React components.

const [result, perform, setSorting, setPage, setPageSize] = AllAccounts.useWithPaging(25);

// Navigate pages
await setPage(result.paging.page + 1);

// Change page size
await setPageSize(50);

// Access paging metadata
const { page, size, totalItems, totalPages } = result.paging;