Implement limit for Rust

backend-rust/step3-finished-app/src/api.rs

@@ -5,8 +5,15 @@ use serde_json::value::RawValue;
 #[derive(Deserialize)]
 #[serde(tag = "action")]
 pub enum Request {
-    Post { message: String, username: String },
-    Fetch { username: Option<String> },
+    Post {
+        message: String,
+        username: String,
+    },
+    Fetch {
+        username: Option<String>,
+        offset: Option<u32>,
+        count: Option<u32>,
+    },
 }
 
 #[derive(Serialize, Debug)]

backend-rust/step3-finished-app/src/lib.rs

@@ -22,7 +22,11 @@ fn run(arg: String) -> String {
     // Parse and username JSON request
     let result = api::parse(arg).and_then(|request| match request {
         Request::Post { message, username } => add_post(message, username),
-        Request::Fetch { username } => fetch_posts(username),
+        Request::Fetch {
+            username,
+            offset,
+            count,
+        } => fetch_posts(username, offset, count),
     });
 
     let result = match result {
@@ -45,12 +49,18 @@ fn add_post(message: String, username: String) -> AppResult<Response> {
     Ok(Response::Post { count })
 }
 
-fn fetch_posts(username: Option<String>) -> AppResult<Response> {
+fn fetch_posts(
+    username: Option<String>,
+    offset: Option<u32>,
+    count: Option<u32>,
+) -> AppResult<Response> {
+    let count = count.unwrap_or(100);
+    let offset = offset.unwrap_or(0);
     let posts_str = match username {
         // Get all posts if no filter username was passed
-        None => model::get_all_posts()?,
+        None => model::get_all_posts(offset, count)?,
         // Or get only posts from specified author
-        Some(h) => model::get_posts_by_username(h)?,
+        Some(h) => model::get_posts_by_username(h, offset, count)?,
     };
 
     // Some Rust-specific detail to play nice with serialization, doesn't matter

backend-rust/step3-finished-app/src/model.rs

@@ -19,21 +19,29 @@ pub fn add_post(message: String, username: String) -> AppResult<()> {
     .map(drop)
 }
 
-pub fn get_all_posts() -> AppResult<String> {
-    database::query(
-        "SELECT json_group_array(
-            json_object('message', message, 'username', username)
-        ) AS json_result FROM (SELECT * FROM messages)",
-    )
-}
-
-pub fn get_posts_by_username(username: String) -> AppResult<String> {
+pub fn get_all_posts(offset: u32, count: u32) -> AppResult<String> {
     database::query(
         format!(
             "SELECT json_group_array(
             json_object('message', message, 'username', username)
-            ) AS json_result FROM (SELECT * FROM messages where username = '{}')",
-            username
+        ) AS json_result FROM (
+            SELECT * FROM messages LIMIT {} OFFSET {}
+        )",
+            count, offset,
+        )
+        .as_str(),
+    )
+}
+
+pub fn get_posts_by_username(username: String, offset: u32, count: u32) -> AppResult<String> {
+    database::query(
+        format!(
+            "SELECT json_group_array(
+            json_object('message', message, 'username', username)
+            ) AS json_result FROM (
+                SELECT * FROM messages where username = '{}' LIMIT {} OFFSET {}    
+            )",
+            username, count, offset
         )
         .as_str(),
     )