Modularize beacon node backend (#4718)

#4669


  Modularize the beacon node backend to make it easier to add new database implementations

beacon_node/store/src/partial_beacon_state.rs

@@ -2,8 +2,8 @@ use crate::chunked_vector::{
     load_variable_list_from_db, load_vector_from_db, BlockRootsChunked, HistoricalRoots,
     HistoricalSummaries, RandaoMixes, StateRootsChunked,
 };
-use crate::{Error, KeyValueStore};
-use ssz::{Decode, DecodeError};
+use crate::{DBColumn, Error, KeyValueStore, KeyValueStoreOp};
+use ssz::{Decode, DecodeError, Encode};
 use ssz_derive::{Decode, Encode};
 use std::sync::Arc;
 use types::historical_summary::HistoricalSummary;
@@ -172,6 +172,15 @@ impl<E: EthSpec> PartialBeaconState<E> {
         ))
     }
 
+    /// Prepare the partial state for storage in the KV database.
+    pub fn as_kv_store_op(&self, state_root: Hash256) -> KeyValueStoreOp {
+        KeyValueStoreOp::PutKeyValue(
+            DBColumn::BeaconState,
+            state_root.as_slice().to_vec(),
+            self.as_ssz_bytes(),
+        )
+    }
+
     pub fn load_block_roots<S: KeyValueStore<E>>(
         &mut self,
         store: &S,