Add maxBatchSize attribute to `@BatchMapping`

[frehov]

Hi, sorry if this has been requested before

As the title suggests, I would like to put forward a feature request for having the @BatchMapping-annotation expose a maxBatchSize which will be set on the default DataLoaderOptions for that DataLoader. As MappingInfo is collected before registration I would carefully suggest that the batchloader boolean be changed to it's own separate object which would enclose additional properties for a batchloader like this.

Annotation annotation = annotations.iterator().next();
if (annotation instanceof SchemaMapping) {
	SchemaMapping mapping = (SchemaMapping) annotation;
	typeName = mapping.typeName();
	field = (StringUtils.hasText(mapping.field()) ? mapping.field() : method.getName());
}
else {
	BatchMapping mapping = (BatchMapping) annotation;
	typeName = mapping.typeName();
	field = (StringUtils.hasText(mapping.field()) ? mapping.field() : method.getName());
	batchMapping = BatchOptions.withMaximumBatchSize(mapping.maxBatchSize);
}

And these changes would be necessary in the MappingInfo class, and the BatchOptions class has been omitted as that would be an implementation detail for the spring team to consider if at all implemented.

private static class MappingInfo {

	private final FieldCoordinates coordinates;

	private final BatchOptions batchOptions;

	private final HandlerMethod handlerMethod;

	public MappingInfo(String typeName, String field, BatchOptions BatchOptions, HandlerMethod handlerMethod) {
		this.coordinates = FieldCoordinates.coordinates(typeName, field);
		this.handlerMethod = handlerMethod;
		this.batchOptions= batchOptions;
	}

	public FieldCoordinates getCoordinates() {
		return this.coordinates;
	}

	@SuppressWarnings("BooleanMethodIsAlwaysInverted")
	public boolean isBatchMapping() {
		return this.batchOptions != null;
	}

        public boolean getBatchOptions() {
                return this.batchOptions;
        }

	public HandlerMethod getHandlerMethod() {
		return this.handlerMethod;
	}

	@Override
	public String toString() {
		return this.coordinates + " -> " + this.handlerMethod;
	}
}

Secondary I would like to suggest the addition of ConfigurationProperties that could act as the "default" DataLoaderOptions and be injected into the BatchLoaderRegistry for convenience to be able to set properties like max batch size globally, perhaps under the key spring.graphql.dataloader.options

[rstoyanchev]

Thanks for the suggestions. Exposing maxBatchSize on @BatchMapping sounds good to me, and so does the second suggestion for default DataLoaderOptions but I've created a separate issue #522 for that.