[*.cs]
dotnet_diagnostic.LC019.severity = error

LC019: Conditional Include Expression

In Plain Terms

Imagine you’re at a restaurant and you tell the waiter “If it’s Tuesday, bring me pizza; otherwise bring me pasta” — but this waiter only understands one order at a time. He gets confused and drops your plate on the floor every single time.

What it flags

Flags conditional logic embedded in EF Core Include paths because include graphs must stay shape-stable to translate reliably and remain predictable. This includes root-level ternary/null-coalescing expressions and conditional receivers inside a longer navigation path.

Why it matters

EF Core expects Include and ThenInclude lambdas to describe a concrete navigation path. Choosing between alternate navigations inside the lambda can fail at runtime or make the eager-loading shape ambiguous. Split the query shape before the Include call so each branch has a normal navigation path.

The problem is not the ?: operator by itself. A conditional inside a filtered Include predicate, ordering selector, or Take argument does not choose between navigation paths, so LC019 leaves those shapes alone.

What it does not flag

LC019 is limited to EF Core Include and ThenInclude calls. It does not report unrelated application extension methods named Include or ThenInclude, and it does not treat conditionals inside filtered Include operators as conditional navigation paths.

Typical fix

Project a conditional shape outside the Include chain, split the query, or load alternate branches explicitly. This rule is manual-only because the correct replacement usually depends on whether both branches should run, whether the branches need different filters, and how the query is composed afterward.

Use this decision path:

1. If exactly one navigation should be eager-loaded, split the query before Include.
2. If both navigations are useful to the caller, eager-load both explicit paths.
3. If the caller only needs scalar values or a small DTO, project the conditional shape with Select instead of using Include.
4. If each branch needs a different filtered Include, keep the filters inside two separate branch-specific Include chains.

Samples

See samples/LinqContraband.Sample/Samples/LC019_ConditionalInclude/ for a focused example.

The crime

var query = db.Orders
    .Include(o => includeCustomer ? o.Customer : o.AlternateCustomer);

var query = db.Orders
    .Include(o => (includePrimary ? o.PrimaryCustomer : o.FallbackCustomer).Address);

var query = db.Orders
    .Include(o => o.Customer)
    .ThenInclude(c => (preferBilling ? c.BillingAddress : c.ShippingAddress).Country);

A better shape

var query = includeCustomer
    ? db.Orders.Include(o => o.Customer)
    : db.Orders.Include(o => o.AlternateCustomer);

var query = includePrimary
    ? db.Orders.Include(o => o.PrimaryCustomer.Address)
    : db.Orders.Include(o => o.FallbackCustomer.Address);

var query = preferBilling
    ? db.Orders.Include(o => o.Customer).ThenInclude(c => c.BillingAddress.Country)
    : db.Orders.Include(o => o.Customer).ThenInclude(c => c.ShippingAddress.Country);

When projection is better

If the conditional is there because the result model needs “the active address” or “the preferred contact”, a projection is often clearer than an Include:

var query = db.Orders.Select(o => new OrderSummary
{
    Id = o.Id,
    Address = preferBilling ? o.Customer.BillingAddress : o.Customer.ShippingAddress
});

Projection keeps the conditional in the result shape, where EF can translate ordinary scalar/entity selection, instead of trying to make the eager-loading graph dynamic.

When eager-loading both branches is better

If the caller will inspect both possible navigations after materialization, include both paths explicitly:

var query = db.Orders
    .Include(o => o.PrimaryCustomer.Address)
    .Include(o => o.FallbackCustomer.Address);

This may load more data, so prefer it only when both branches are genuinely needed. If only one branch is used per request, split before Include instead.

Filtered Include boundary

Conditionals inside filtered Include operators are allowed because they do not change the navigation path:

var query = db.Orders.Include(o => o.Lines
    .Where(l => priorityOnly ? l.IsPriority : l.IsBackordered)
    .OrderBy(l => newestFirst ? l.CreatedAt : l.Id)
    .Take(shortList ? 5 : 10));

The navigation path remains Orders -> Lines; only the filter/order/window changes.