protected override Expression BuildSerializerSafe(Expression encoder, Expression value)
{
// Indexing schemas according to their position.
// according to avro spec http://avro.apache.org/docs/current/spec.html#Unions
// Unions may not contain more than one schema with the same type, except for the named types record, fixed and enum.
// For example, unions containing two array types or two map types are not permitted, but two types with different names are permitted
int schemaIndex = 0;
var schemas = new List <IndexedSchema>(this.itemSchemas.Count);
foreach (var typeSchema in this.itemSchemas)
{
// use FirstOrDefault rather than SingleOrDefault because we need to add all schema to the list.
var existingSchema = schemas.FirstOrDefault(s => UnionSchema.IsSameTypeAs(s.Schema, typeSchema));
var index = existingSchema != null ? existingSchema.Index : schemaIndex++;
var indexSchema = new IndexedSchema {
Schema = typeSchema, Index = index
};
schemas.Add(indexSchema);
}
// Nullable schemas.
if (schemas.Count == 2 && schemas.Select(s => s.Schema).OfType <NullSchema>().Any())
{
return(this.BuildNullableSerializer(encoder, value, schemas));
}
// Sort according to inheritance hierarchy - most specialized type goes first.
schemas.Sort(this.MoreSpecializedTypesFirst);
return(this.BuildUnionSerializer(encoder, value, schemas));
}
private int MoreSpecializedTypesFirst(IndexedSchema s1, IndexedSchema s2)
{
if (s1.Schema.RuntimeType.IsAssignableFrom(s2.Schema.RuntimeType))
{
return(1);
}
if (s2.Schema.RuntimeType.IsAssignableFrom(s1.Schema.RuntimeType))
{
return(-1);
}
return(s1.Index.CompareTo(s2.Index));
}
