Projections & Streaming

Projections

Project query results into a different shape at the SQL level via json_object — no full document deserialization needed.

// Flat projection
var results = await store.Query<User, UserSummary>(
    u => u.Age == 25,
    u => new UserSummary { Name = u.Name, Email = u.Email },
    ctx.User,
    ctx.UserSummary);

// Nested source properties
var results = await store.Query<Order, OrderSummary>(
    o => o.Status == "Shipped",
    o => new OrderSummary { Customer = o.CustomerName, City = o.ShippingAddress.City },
    ctx.Order,
    ctx.OrderSummary);

// GetAll with projection
var results = await store.GetAll<Order, OrderDetail>(
    o => new OrderDetail { Customer = o.CustomerName, LineCount = o.Lines.Count() },
    ctx.Order,
    ctx.OrderDetail);

// Collection methods in projections: Count(), Any(), Count(predicate), Any(predicate)
o => new OrderDetail { HasLines = o.Lines.Any(), GadgetCount = o.Lines.Count(l => l.ProductName == "Gadget") }

Projection expressions reference

Expression	SQL Output
`x => new R { A = x.Name }`	`json_object('name', json_extract(Data, '$.name'))`
`x => new R { C = x.Nav.Prop }`	`json_object('c', json_extract(Data, '$.nav.prop'))`
`x => new R { N = x.Lines.Count() }`	`json_array_length(Data, '$.lines')`
`x => new R { N = x.Lines.Count(l => ...) }`	`(SELECT COUNT(*) FROM json_each(Data, '$.lines') WHERE ...)`
`x => new R { B = x.Tags.Any() }`	`CASE WHEN json_array_length(...) > 0 THEN json('true') ELSE json('false') END`
`x => new R { B = x.Tags.Any(t => ...) }`	`CASE WHEN EXISTS (...) THEN json('true') ELSE json('false') END`

Streaming

All list-returning methods have IAsyncEnumerable<T> streaming counterparts that yield results one-at-a-time without buffering.

// Stream all documents
await foreach (var user in store.GetAllStream<User>(ctx.User))
{
    Console.WriteLine(user.Name);
}

// Stream with expression filter
await foreach (var user in store.QueryStream<User>(u => u.Age > 30, ctx.User))
{
    Console.WriteLine(user.Name);
}

// Stream with projection
await foreach (var summary in store.GetAllStream<Order, OrderSummary>(
    o => new OrderSummary { Customer = o.CustomerName, City = o.ShippingAddress.City },
    ctx.Order,
    ctx.OrderSummary))
{
    Console.WriteLine($"{summary.Customer} in {summary.City}");
}

// Stream with raw SQL
await foreach (var user in store.QueryStream<User>(
    "json_extract(Data, '$.name') = @name",
    ctx.User,
    new { name = "Alice" }))
{
    Console.WriteLine(user.Name);
}