Leptos-Struct-Table: Fix Excessive Get_page Calls

by Rajiv Sharma 50 views

Hey guys,

Let's dive into an interesting issue one of our community members encountered while using the leptos-struct-table crate, specifically with the PaginatedTableDataProvider. This crate looks super promising for creating interactive tables in Leptos, but as with any new tool, there can be some quirks to iron out. We'll break down the problem, explore the code, and understand why get_page might be getting called more than you'd expect. Buckle up!

Understanding the Issue: Too Many get_page Calls

The main issue reported is that the get_page method within the PaginatedTableDataProvider trait is being called for a range of page indexes, even when only the first page is necessary. This can lead to unnecessary data fetching and potentially impact performance. Let's understand the core problem first.

The Scenario

Imagine you have a table displaying a list of games. You're using the PaginatedTableDataProvider to handle pagination, meaning you're loading data in chunks or pages. You've set up your table to display 20 rows per page, and your dataset contains, say, 20 games in total. Logically, you'd only expect the get_page method to be called once, for the first page (index 0). However, what's happening is that get_page gets called for indexes 0, 1, 2, 3, and 4, and even repeats some of these calls. That's not ideal, right?

Code Snippet

To illustrate this, let's look at the code snippet provided by the user. Here’s how the GamesDataProvider is implemented:

impl PaginatedTableDataProvider<Game> for GamesDataProvider {
    const PAGE_ROW_COUNT: usize = 20;

    async fn get_page(&self, page_index: usize) -> Result<Vec<Game>, String> {
        log::info!("get_page {page_index}");
        if page_index == 0 {
            Ok(self.games.clone())
        } else {
            Ok(vec![])
        }
    }

    async fn row_count(&self) -> Option<usize> {
        log::info!("row_count");
        Some(self.games.len())
    }
}

In this setup, the get_page function logs the page index being requested. If the index is 0, it returns the list of games; otherwise, it returns an empty vector. The row_count function simply returns the total number of games.

The table is displayed using the following Leptos view:

    let games = move || GamesDataProvider::new();

    let pagination_controller = PaginationController::default();
    let container = NodeRef::new();

    view! {
        <div class="lg:flex lg:items-center lg:justify-center m-8" node_ref=container>
            <table class="text-sm text-left text-gray-400">
                <TableContent
                    rows=games()
                    display_strategy=DisplayStrategy::Pagination {
                        controller: pagination_controller,
                        row_count: 20,
                    }
                    scroll_container=container
                />
            </table>
        </div>
    }

Here, a TableContent component is used with a pagination display strategy. The row_count is set to 20, matching the PAGE_ROW_COUNT in the data provider.

Observed Behavior

With these parameters, one would expect get_page to be called only for index 0. However, the logs show that get_page is called repeatedly for indexes 0, 1, 2, 3, and 4. This behavior is definitely not what we want, and let’s discuss why this might be happening.

Diving Deeper: Why Are These Extra Calls Happening?

To really understand why get_page is being called so many times, we need to think about how the leptos-struct-table crate handles pagination. There are a couple of potential reasons for this behavior:

  1. Initial Rendering and Calculations: The table might be initially rendering and calculating the number of pages needed. During this process, it might be querying for multiple pages to determine the total number of rows or adjust the pagination controls. Think of it like the table trying to figure out how many pages it could have, even if it doesn't need them all right away.
  2. Component Lifecycle and Reactivity: Leptos, like other reactive frameworks, re-renders components when their dependencies change. If the pagination state (e.g., current page, total pages) is being updated, it could trigger additional calls to get_page. It's possible that some internal logic within the table component or pagination controller is causing these updates.
  3. Scroll Handling: The use of scroll_container suggests that the table might be trying to pre-fetch data as the user scrolls. Even if there's no actual scrolling happening, the initial setup might be triggering these pre-fetches.

Digging into the Code

To get a definitive answer, we'd need to delve into the source code of leptos-struct-table, specifically the TableContent component and the PaginationController. Looking at how these components interact and how they call the PaginatedTableDataProvider methods would likely reveal the root cause. For example, we could inspect:

  • How the total number of pages is calculated.
  • When and how the get_page method is called.
  • How the pagination controls are updated and if these updates trigger re-renders.

Possible Misuse of the API?

The user who reported the issue also wondered if they were misusing the API. While their code looks pretty standard and closely follows the example provided in the leptos-struct-table repository, it's always worth double-checking. Here are a few things to consider:

  • Correctness of row_count: Make sure the row_count function accurately returns the total number of rows. If this value is incorrect, the table might miscalculate the number of pages.
  • Pagination Controller: Ensure the PaginationController is being used correctly. Are there any manual updates to the controller that might be causing issues?
  • Data Provider Logic: Review the logic in your get_page function. While the provided code seems straightforward, any unexpected behavior there could lead to problems.

Reproducing the Issue: The Minimal Example

The user was kind enough to provide a minimal example to reproduce the issue, which is super helpful for debugging. This example (test-leptos-table.tar.gz) allows us to run the code locally and observe the same behavior. By stepping through the code and adding more logging statements, we can pinpoint exactly where the extra get_page calls are originating from.

Steps to Reproduce

  1. Download the test-leptos-table.tar.gz archive.
  2. Extract the contents.
  3. Navigate to the project directory.
  4. Run the application (likely using cargo run or a similar command).
  5. Observe the logs and see the repeated calls to get_page.

Debugging Tips

When debugging this issue, consider these strategies:

  • Add More Logging: Insert log::info! statements in various parts of the TableContent component and the PaginationController to track the flow of execution and the values of relevant variables.
  • Use a Debugger: If you're comfortable with a debugger, step through the code to see exactly when and why get_page is being called.
  • Simplify the Example: Try simplifying the example further. For instance, remove the scroll container or reduce the number of rows to see if the behavior changes.

Potential Solutions and Workarounds

While we haven't pinpointed the exact cause yet, there are a few potential solutions or workarounds we can consider:

  1. Optimize Initial Rendering: If the extra calls are happening during initial rendering, we might be able to optimize the component to avoid unnecessary calculations or data fetching. This could involve using more efficient algorithms or delaying certain operations until they are actually needed.
  2. Control Reactivity: If reactivity is the issue, we might need to fine-tune how the pagination state is managed and updated. This could involve using memo or other techniques to prevent unnecessary re-renders.
  3. Lazy Loading: If pre-fetching due to scroll handling is the problem, we could implement a more intelligent lazy loading strategy that only fetches data when it's actually close to being visible.
  4. Cache Results: A simple workaround could be to cache the results of get_page. If the same page is requested multiple times, we can return the cached data instead of making another API call. This won't solve the underlying issue, but it can mitigate the performance impact.

Conclusion: Let's Crack This Together

The issue of excessive get_page calls in leptos-struct-table's PaginatedTableDataProvider is an intriguing one. While we don't have a definitive answer yet, we've explored the problem, examined the code, and discussed potential causes and solutions. The key takeaway here is that by understanding how pagination works and how reactive frameworks like Leptos handle updates, we can better diagnose and fix these kinds of issues.

The next steps would be to dive deeper into the leptos-struct-table source code, reproduce the issue locally, and try out some of the debugging tips mentioned above. Remember, open-source is all about collaboration, so let’s work together to make this awesome crate even better! If you've experienced this issue or have any insights, please share your thoughts in the comments below. Let's get this sorted, guys!