Class ReadModelCollectionsNeverNullConvention

Namespace

Cratis.Arc.MongoDB

Assembly

Cratis.Arc.MongoDB.dll

Represents a MongoDB.Bson.Serialization.Conventions.IMemberMapConvention that materializes a read model's declared non-nullable collection members as empty collections rather than null.

public class ReadModelCollectionsNeverNullConvention : ConventionBase, IMemberMapConvention, IConvention

Inheritance

object

ConventionBase

ReadModelCollectionsNeverNullConvention

Implements

IMemberMapConvention

IConvention

Inherited Members

ConventionBase.Name

object.GetType()

object.MemberwiseClone()

object.ToString()

object.Equals(object)

object.Equals(object, object)

object.ReferenceEquals(object, object)

object.GetHashCode()

Extension Methods

MethodCalls.CallGenericMethod<TOut, T>(T, Expression<Func<T, Func<TOut>>>, params Type[])

MethodCalls.CallGenericMethod<TOut, T, T1>(T, Expression<Func<T, Func<T1, TOut>>>, T1, params Type[])

MethodCalls.CallGenericMethod<TOut, T, T1, T2>(T, Expression<Func<T, Func<T1, T2, TOut>>>, T1, T2, params Type[])

MethodCalls.CallGenericMethod<TOut, T, T1, T2, T3>(T, Expression<Func<T, Func<T1, T2, T3, TOut>>>, T1, T2, T3, params Type[])

ConverterExtensions.ConvertTo(object, Type)

ConceptExtensions.GetConceptValue(object)

ConceptExtensions.IsConcept(object)

JsonValueExtensions.ToJsonValue(object?)

ObservableExtensions.InvokeAndWrapWithSubject<TResult>(object, Func<CancellationToken, IObservable<TResult>>)

ObservableExtensions.InvokeAndWrapWithTransformSubject<TResult, TSource>(object, Func<CancellationToken, IObservable<TSource>>, Func<TSource, TResult>)

Remarks

A read model that declares a child collection as a non-nullable IEnumerable<T> promises the type system that the value is there. A store is free to disagree: Chronicle's read model sink writes no field at all for a child collection that has never had an element, and can write an explicit null for one whose last element went away. Either way the driver hands back null for a member nullable analysis has already concluded can never be null, so an unguarded .Any() or .Select() throws where nothing warned it might.

Chronicle closes this for its own reader through a JsonTypeInfo modifier on the client's serializer options. That fix is confined to Chronicle's serialization boundary and never reaches the MongoDB driver — which is the sanctioned path for reading a read model by anything other than its key, and the one Arc's own server-side paging runs on. This convention is the same guarantee, restated where the driver can honor it.

Only members the declaration says cannot be null are touched. A member declared IEnumerable<T>? keeps the distinction between "no collection" and "an empty collection", because that model asked for it. Dictionaries are left alone — an absent map is not the same defect — and string is excluded despite being an IEnumerable. A member that carries its own MongoDB.Bson.Serialization.Attributes.BsonDefaultValueAttribute has stated what it wants and is skipped entirely.

The convention is registered under ReadModelCollectionsNeverNull and scoped to [ReadModel] types, so it can be turned off per type with [IgnoreConventions(ConventionPacks.ReadModelCollectionsNeverNull)].

Constructors

ReadModelCollectionsNeverNullConvention()

public ReadModelCollectionsNeverNullConvention()

Methods

Apply(BsonMemberMap)

Applies the convention to a member map, giving a declared non-nullable collection an empty value for both an absent element and a stored null.

public void Apply(BsonMemberMap memberMap)

Parameters

memberMap BsonMemberMap

The MongoDB.Bson.Serialization.BsonMemberMap to apply to.