Add Guard::into_inner_if_some

src/blob_tree/mod.rs

@@ -58,6 +58,27 @@ impl IterGuard for Guard {
         }
     }
 
+    fn into_inner_if_some<T>(
+        self,
+        pred: impl Fn(&UserKey) -> Option<T>,
+    ) -> crate::Result<Option<(T, UserValue)>> {
+        let kv = self.kv?;
+
+        if let Some(t) = pred(&kv.key.user_key) {
+            resolve_value_handle(
+                self.tree.id(),
+                self.tree.blobs_folder.as_path(),
+                &self.tree.index.config.cache,
+                &self.tree.index.config.descriptor_table,
+                &self.version,
+                kv,
+            )
+            .map(|(_, v)| Some((t, v)))
+        } else {
+            Ok(None)
+        }
+    }
+
     fn key(self) -> crate::Result<UserKey> {
         self.kv.map(|kv| kv.key.user_key)
     }

src/iter_guard.rs

@@ -19,6 +19,19 @@ pub trait IterGuard {
         pred: impl Fn(&UserKey) -> bool,
     ) -> crate::Result<(UserKey, Option<UserValue>)>;
 
+    /// Accesses the key-value pair if the predicate returns `Some(T)`.
+    ///
+    /// The predicate receives the key - if returning None, the value
+    /// may not be loaded if the tree is key-value separated.
+    ///
+    /// # Errors
+    ///
+    /// Will return `Err` if an IO error occurs.
+    fn into_inner_if_some<T>(
+        self,
+        pred: impl Fn(&UserKey) -> Option<T>,
+    ) -> crate::Result<Option<(T, UserValue)>>;
+
     /// Accesses the key-value pair.
     ///
     /// # Errors

src/tree/mod.rs

@@ -49,6 +49,19 @@ impl IterGuard for Guard {
         }
     }
 
+    fn into_inner_if_some<T>(
+        self,
+        pred: impl Fn(&UserKey) -> Option<T>,
+    ) -> crate::Result<Option<(T, UserValue)>> {
+        let (k, v) = self.0?;
+
+        if let Some(t) = pred(&k) {
+            Ok(Some((t, v)))
+        } else {
+            Ok(None)
+        }
+    }
+
     fn key(self) -> crate::Result<UserKey> {
         self.0.map(|(k, _)| k)
     }

tests/guard_if.rs

@@ -69,3 +69,80 @@ fn guard_into_inner_if_blob() -> lsm_tree::Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn guard_into_inner_if_some() -> lsm_tree::Result<()> {
+    let folder = get_tmp_folder();
+
+    {
+        let tree = Config::new(
+            &folder,
+            SequenceNumberCounter::default(),
+            SequenceNumberCounter::default(),
+        )
+        .open()?;
+
+        tree.insert("earth#name", "earth", 0);
+        tree.insert("earth#color", "BLUE", 0);
+
+        assert_eq!(2, tree.iter(SeqNo::MAX, None).count());
+
+        assert_eq!(
+            1,
+            tree.iter(SeqNo::MAX, None)
+                .filter_map(|guard| {
+                    guard
+                        .into_inner_if_some(|key| {
+                            if key.ends_with(b"#name") {
+                                Some(())
+                            } else {
+                                None
+                            }
+                        })
+                        .unwrap()
+                })
+                .count(),
+        );
+    }
+
+    Ok(())
+}
+
+#[test]
+fn guard_into_inner_if_some_blob() -> lsm_tree::Result<()> {
+    let folder = get_tmp_folder();
+
+    {
+        let tree = Config::new(
+            &folder,
+            SequenceNumberCounter::default(),
+            SequenceNumberCounter::default(),
+        )
+        .with_kv_separation(Some(KvSeparationOptions::default().separation_threshold(1)))
+        .open()?;
+
+        tree.insert("earth#name", "earth", 0);
+        tree.insert("earth#color", "BLUE", 0);
+
+        assert_eq!(2, tree.iter(SeqNo::MAX, None).count());
+
+        assert_eq!(
+            1,
+            tree.iter(SeqNo::MAX, None)
+                .filter_map(|guard| {
+                    guard
+                        .into_inner_if_some(|key| {
+                            if key.ends_with(b"#name") {
+                                Some(())
+                            } else {
+                                None
+                            }
+                        })
+                        .unwrap()
+                })
+                .count(),
+        );
+    }
+
+    Ok(())
+}