DKNet

Build runtime predicates

Part of DKNet.EfCore.Specifications. For caller-supplied criteria, validate the triple before using it. In the Quick Start, add using LinqKit; and using DKNet.EfCore.Specifications.Dynamics;, then query:

if (!DynamicPredicateExtensions.TryBuildPredicate<Product>("price", Ops.GreaterThanOrEqual, "10", out var filter))
    throw new ArgumentException("Invalid price filter.");
var matches = await db.Products.AsExpandable().Where(filter!).ToListAsync();
Console.WriteLine(matches.Single().Name); // Coffee

TryBuildPredicate validates an operation and normalized property path, coerces values, and returns a parsed predicate or false before the caller chooses whether to accept the filter.

DynamicAnd/DynamicOr in namespace LinqKit accept either ExpressionStarter<T> or Expression<Func<T, bool>>. Their typed (propertyName, Ops, value) overloads return the predicate unchanged for unusable conditions. Use TryBuildPredicate at a request boundary so invalid conditions cannot silently widen the result set.

Ops	Behavior
Equal / NotEqual	Equality; a null value produces a null comparison.
GreaterThan / GreaterThanOrEqual / LessThan / LessThanOrEqual	Ordered comparison.
Contains / NotContains / StartsWith / EndsWith	String operations; non-string targets adjust to equality/inequality.
In / NotIn	Non-empty collection membership, excluding a scalar string.
IsNull / IsNotNull	Null test; supplied value is ignored, and unsupported non-nullable targets fail validation.

Paths normalize camelCase, snake_case and kebab-case segments to PascalCase, including dotted paths. Scalar conversion supports numeric types, booleans, date/time types, Guid and enums. String collections for In/NotIn are converted element by element; already-typed collections must match the target, and unknown enum names are rejected. Out-of-range numeric strings pass Enum.TryParse and are not rejected. Typed filter values are parameterized for EF query-plan reuse.

🧱 Where it fits

A validated predicate enters a specification or an expandable DbSet query, then EF composes it into SQL when materialized.

Repository queries already call AsExpandable(). Raw DbSet/IQueryable paths must call it themselves when composing LinqKit expressions.

⚠️ Gotchas & limits

Invalid operations, unsafe/unknown paths, failed coercion and parse failures yield false from TryBuildPredicate or silently skip the typed DynamicAnd/DynamicOr condition. Neither is automatic request validation.
Do not skip null values indiscriminately: Equal/NotEqual and IsNull/IsNotNull have meaningful null behavior.
The raw (string expression, params object?[] values) overload uses a blocklist and can throw ArgumentException or Dynamic LINQ parse exceptions. Keep expression structure under application control; a blocklist is not an authorization policy.
Validate allowed fields in the host as well as type validity. Successful parsing does not grant permission to filter on a sensitive field.

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