diff --git a/src/item.rs b/src/item.rs
index 15c0deb..af2acce 100644
--- a/src/item.rs
+++ b/src/item.rs
@@ -5,11 +5,6 @@ use mongodb::{bson::doc, ClientSession, Collection};
 
 // todo : api key auth
 
-// case: export
-// used an item -> demand
-// mark as used
-// update db
-
 // ITEM
 // VARIANTS
 // QUANTIZATION
@@ -30,6 +25,13 @@ macro_rules! collect_results {
     }};
 }
 
+macro_rules! cdb_col {
+    ($db:expr, $col:expr) => {
+        $db.database("cdb")
+            .collection::<mongodb::bson::Document>($col)
+    };
+}
+
 macro_rules! get_mongo {
     () => {
         mongodb::Client::with_uri_str(std::env::var("DB_URI").unwrap())
@@ -360,9 +362,37 @@ impl Transaction {
 }
 
 impl Variant {
-    pub async fn demand(&self, uuid: &str) -> String {
-        // todo : transaction_out + receipt
-        todo!()
+    pub async fn demand(&self, uuid: &str, price: Price, destination: String) -> Option<String> {
+        let db = get_mongo!();
+
+        // check if supply transaction exists
+        let supply_t = cdb_col!(db, "supply");
+        if supply_t
+            .find_one(doc! { "_id": uuid }, None)
+            .await
+            .unwrap()
+            .is_none()
+        {
+            return None;
+        }
+
+        // todo : demand batch
+
+        // mark as used
+        let demand_t = cdb_col!(db, "demand");
+        demand_t
+            .insert_one(
+                doc! {
+                    "_id": uuid,
+                    "destination": destination,
+                    "price": price.as_bson()
+                },
+                None,
+            )
+            .await
+            .unwrap();
+
+        Some(uuid.to_string())
     }
 
     /// Records a supply transaction in the database.
@@ -382,7 +412,7 @@ impl Variant {
         let mut ses = db.start_session(None).await.unwrap();
 
         let col: mongodb::Collection<mongodb::bson::Document> =
-            ses.client().database("cdb").collection("transactions");
+            ses.client().database("cdb").collection("supply");
 
         let mut transactions = vec![];
         for _ in 0..amount {