Say I have a `StorageDoubleMap` that stores `Data` structs for each user and `ContextId`
```rust
	#[pallet::storage]
	pub type Info<T: Config> = StorageDoubleMap<
		_,
		Blake2_128Concat,
		T::AccountId,
		Twox64Concat,
		T::ContextId,
		Data,
	>;
```
Is there an option to limit the amount of entries per `AccountId`? Or should I keep a count of entries in a separate map?

**Update**:

Accessing a specific `ContextId` for an `AccountId` quickly is important to me, that's why I chose `StorageDoubleMap`.

Moreover, a common operation will be to iterate over all `ContextId`s for an `AccountId`, which `StorageDoubleMap` also [has support for](https://docs.rs/frame-support/latest/frame_support/storage/types/struct.StorageDoubleMap.html#method.iter_prefix).