diff --git a/src/backends/ntriples.rs b/src/backends/ntriples.rs
index 0711aaa..9b33b4d 100644
--- a/src/backends/ntriples.rs
+++ b/src/backends/ntriples.rs
@@ -64,47 +64,59 @@ impl Backend for NTriples {
                 Err(_) => return Err(format!("Error retrieving the {}th row", i)),
             };
 
-            if let Err(_) = formatter.format(&Triple {
-                subject: match row.get(0) {
-                    Some(subject) => match subject {
-                        AnyValue::Utf8(iri) => NamedNode {
-                            iri: &iri[1..iri.len() - 1],
+            if formatter
+                .format(&Triple {
+                    subject: match row.get(0) {
+                        Some(subject) => match subject {
+                            AnyValue::Utf8(iri) => NamedNode {
+                                iri: &iri[1..iri.len() - 1],
+                            }
+                            .into(),
+                            _ => {
+                                return Err(format!("Cannot parse from non-string at {}th row", i))
+                            }
+                        },
+                        None => {
+                            return Err(format!("Error obtaining the subject of the {}th row", i))
                         }
-                        .into(),
-                        _ => return Err(format!("Cannot parse from non-string at {}th row", i)),
                     },
-                    None => return Err(format!("Error obtaining the subject of the {}th row", i)),
-                },
-                predicate: match row.get(1) {
-                    Some(predicate) => match predicate {
-                        AnyValue::Utf8(iri) => NamedNode {
-                            iri: &iri[1..iri.len() - 1],
+                    predicate: match row.get(1) {
+                        Some(predicate) => match predicate {
+                            AnyValue::Utf8(iri) => NamedNode {
+                                iri: &iri[1..iri.len() - 1],
+                            },
+                            _ => {
+                                return Err(format!("Cannot parse from non-string at {}th row", i))
+                            }
+                        },
+                        None => {
+                            return Err(format!("Error obtaining the predicate of the {}th row", i))
                         }
-                        .into(),
-                        _ => return Err(format!("Cannot parse from non-string at {}th row", i)),
                     },
-                    None => {
-                        return Err(format!("Error obtaining the predicate of the {}th row", i))
-                    }
-                },
-                object: match row.get(2) {
-                    Some(object) => match object {
-                        AnyValue::Utf8(iri) => NamedNode {
-                            iri: &iri[1..iri.len() - 1],
+                    object: match row.get(2) {
+                        Some(object) => match object {
+                            AnyValue::Utf8(iri) => NamedNode {
+                                iri: &iri[1..iri.len() - 1],
+                            }
+                            .into(),
+                            _ => {
+                                return Err(format!("Cannot parse from non-string at {}th row", i))
+                            }
+                        },
+                        None => {
+                            return Err(format!("Error obtaining the object of the {}th row", i))
                         }
-                        .into(),
-                        _ => return Err(format!("Cannot parse from non-string at {}th row", i)),
                     },
-                    None => return Err(format!("Error obtaining the object of the {}th row", i)),
-                },
-            }) {
+                })
+                .is_err()
+            {
                 return Err(format!("Error parsing the {}th row", i));
             }
         }
 
         match formatter.finish() {
             Ok(_) => Ok(()),
-            Err(_) => return Err(format!("Error storing the results to the file")),
+            Err(_) => Err(String::from("Error storing the results to the file")),
         }
     }
 }
diff --git a/src/backends/parquet.rs b/src/backends/parquet.rs
index f4ca51c..6ccb2da 100644
--- a/src/backends/parquet.rs
+++ b/src/backends/parquet.rs
@@ -12,13 +12,13 @@ impl Backend for Parquet {
         todo!()
     }
 
-    fn export(path: &str, mut df: &mut DataFrame) -> Result<(), String> {
+    fn export(path: &str, df: &mut DataFrame) -> Result<(), String> {
         let buffer = match File::create(path) {
             Ok(buffer) => buffer,
             Err(_) => return Err(String::from("Error creating the Parquet file")),
         };
 
-        match ParquetWriter::new(buffer).finish(&mut df) {
+        match ParquetWriter::new(buffer).finish(df) {
             Ok(_) => Ok(()),
             Err(_) => Err(String::from("Error writing to the Parquet file")),
         }
diff --git a/src/pschema.rs b/src/pschema.rs
index 6db667b..fd0019a 100644
--- a/src/pschema.rs
+++ b/src/pschema.rs
@@ -105,7 +105,7 @@ impl<T: Literal + Clone> PSchema<T> {
                         .gt(lit(0)),
                 )
                 .left_join(
-                    graph.to_owned().edges.lazy(),
+                    graph.edges.lazy(),
                     Column::VertexId.as_ref(),
                     Column::Subject.as_ref(),
                 )