Add swap and decode_len to DoubleMap

node/runtime/src/lib.rs

@@ -84,8 +84,8 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to equal spec_version. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 170,
-	impl_version: 170,
+	spec_version: 171,
+	impl_version: 171,
 	apis: RUNTIME_API_VERSIONS,
 };
 

srml/support/src/storage/generator/double_map.rs

@@ -17,7 +17,7 @@
 use rstd::prelude::*;
 use rstd::borrow::Borrow;
 use codec::{Ref, FullCodec, FullEncode, Encode, EncodeLike, EncodeAppend};
-use crate::{storage::{self, unhashed}, hash::StorageHasher};
+use crate::{storage::{self, unhashed}, hash::StorageHasher, traits::Len};
 
 /// Generator for `StorageDoubleMap` used by `decl_storage`.
 ///
@@ -116,6 +116,27 @@ where
 		G::from_optional_value_to_query(value)
 	}
 
+	fn swap<KArg1, KArg2>(key11: KArg1, key12: KArg2, key21: KArg1, key22: KArg2)
+	where
+		KArg1: EncodeLike<K1>,
+		KArg2: EncodeLike<K2>,
+	{
+		let final_k1 = Self::storage_double_map_final_key(key11, key12);
+		let final_k2 = Self::storage_double_map_final_key(key21, key22);
+
+		let v1 = unhashed::get_raw(&final_k1);
+		if let Some(val) = unhashed::get_raw(&final_k2) {
+			unhashed::put_raw(&final_k1, &val);
+		} else {
+			unhashed::kill(&final_k1)
+		}
+		if let Some(val) = v1 {
+			unhashed::put_raw(&final_k2, &val);
+		} else {
+			unhashed::kill(&final_k2)
+		}
+	}
+
 	fn insert<KArg1, KArg2, VArg>(k1: KArg1, k2: KArg2, val: VArg)
 	where
 		KArg1: EncodeLike<K1>,
@@ -204,4 +225,21 @@ where
 		Self::append(Ref::from(&k1), Ref::from(&k2), items.clone())
 			.unwrap_or_else(|_| Self::insert(k1, k2, items));
 	}
+
+	fn decode_len<KArg1, KArg2>(key1: KArg1, key2: KArg2) -> Result<usize, &'static str>
+		where KArg1: EncodeLike<K1>,
+		      KArg2: EncodeLike<K2>,
+		      V: codec::DecodeLength + Len,
+	{
+		let final_key = Self::storage_double_map_final_key(key1, key2);
+		if let Some(v) = unhashed::get_raw(&final_key) {
+			<V as codec::DecodeLength>::len(&v).map_err(|e| e.what())
+		} else {
+			let len = G::from_query_to_optional_value(G::from_optional_value_to_query(None))
+				.map(|v| v.len())
+				.unwrap_or(0);
+
+			Ok(len)
+		}
+	}
 }

srml/support/src/storage/mod.rs

@@ -226,6 +226,12 @@ pub trait StorageDoubleMap<K1: FullEncode, K2: FullEncode, V: FullCodec> {
 		KArg1: EncodeLike<K1>,
 		KArg2: EncodeLike<K2>;
 
+	/// Swap the values of two key-pairs.
+	fn swap<KArg1, KArg2>(key11: KArg1, key12: KArg2, key21: KArg1, key22: KArg2)
+	where
+		KArg1: EncodeLike<K1>,
+		KArg2: EncodeLike<K2>;
+
 	fn insert<KArg1, KArg2, VArg>(k1: KArg1, k2: KArg2, val: VArg)
 	where
 		KArg1: EncodeLike<K1>,
@@ -272,4 +278,17 @@ pub trait StorageDoubleMap<K1: FullEncode, K2: FullEncode, V: FullCodec> {
 		V: EncodeAppend<Item=Item>,
 		Items: IntoIterator<Item=EncodeLikeItem> + Clone + EncodeLike<V>,
 		Items::IntoIter: ExactSizeIterator;
+
+	/// Read the length of the value in a fast way, without decoding the entire value.
+	///
+	/// `T` is required to implement `Codec::DecodeLength`.
+	///
+	/// Note that `0` is returned as the default value if no encoded value exists at the given key.
+	/// Therefore, this function cannot be used as a sign of _existence_. use the `::exists()`
+	/// function for this purpose.
+	fn decode_len<KArg1, KArg2>(key1: KArg1, key2: KArg2) -> Result<usize, &'static str>
+		where
+			KArg1: EncodeLike<K1>,
+			KArg2: EncodeLike<K2>,
+			V: codec::DecodeLength + Len;
 }