
# Event Indexers

If you come from Solidity, you’ll know that Solidity allows you to create indexed parameters in your contract events. The indexed parameters allow you to search for these events using the parameters as filters.

While StarkNet does not currently allow you to create indexed parameters by default in Cairo you can index your events using some available indexers such as **[Apibara](https://www.apibara.com/)** and **[StarkNet Indexer](https://github.com/olegabu/starknet-archive-docs#starknet-indexer)**.


## StarkNet Indexer

**StarkNet indexer** is a service created to listen to blockchain events and decode and persist the emitted data, making it available for analysis with SQL, GraphQL, and HTTP queries.

They’ve also created a **[GraphQL console](https://summary.dev/console/)** that enables developers to query blockchain data for events, transactions and their inputs, as well as to filter, aggregate, and sum up values easily.


## Apibara


**Apibara** is a framework and protocol that helps you build real-time, composable streams of Web3 and Web2 data. Apibara solves the challenge of streaming blockchain data: blocks are not immutable, and their data can be invalidated in response to a chain reorganization.

There’s an amazing template to help you get started indexing events [**here**](https://github.com/apibara/python-indexer-template) and a tutorial guide [**here**](https://www.apibara.com/docs/tutorials/indexing-starknet-nft-events).

Swagtimus.eth

What are Event Indexers in Cairo lang? What is a StarkNet indexer?
Can you explain more about how it work and is there any difference between StarkNet indexer and Solidity once?

Newton

What are Event Indexers in Cairo lang? What is a StarkNet indexer?

# Hello starknet fam!

I heard with the last release of protostar it is now possible to make multiple call to different contracts functions in one protostar invoke CLI.

Can someone show me a good exemple on how to use it?

Like multicall with approve and swap.

Thank you very much!

How to use multicall with protostar 0.9.0?

Hello! This is day 12 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Structs.  Perhaps you can help me?

```
// In this challenge you're going to implement a stack using a linked list.
//
// Add the missing code so that main() runs successfully.

from starkware.cairo.common.registers import get_fp_and_pc

struct Node {
    // A pointer to the next node in the stack.
    next: Node*,

    // The value of the node.
    value: felt,

    // The number of elements in the stack.
    size: felt,
}

// Returns an empty stack.
func empty_stack() -> (stack: Node*) {
    alloc_locals;
    local new_node: Node;
    assert new_node.next = cast(0, Node*);
    assert new_node.value = 0;
    assert new_node.size = 0;

    // The usage of get_fp_and_pc() here is necessary in order
    // to access the address of a local variable (&new_node).
    // You can read more about get_fp_and_pc() [here](https://cairo-lang.org/docs/how_cairo_works/functions.html#retrieving-registers).
    let (local __fp__, _) = get_fp_and_pc();
    return (stack=&new_node);
}

// Adds a node to the top of the stack.
// Returns the updated stack (since Cairo is immutable, you can still use the
// old copy of the stack).
func push(stack: Node*, value: felt) -> (stack: Node*) {
    alloc_locals;
    local new_node: Node;
    // Fix and uncomment below.
    // assert new_node.next = ...
    // assert new_node.value = ...
    // assert new_node.size = ...

    let (__fp__, _) = get_fp_and_pc();
    return (stack=&new_node);
}

// Removes the top element of the stack.
// Returns the updated stack and the element that was removed.
func pop(stack: Node*) -> (stack: Node*, value: felt) {
    return (stack=stack.next, value=stack.value);
}

// Returns the value of the n-th element from the top of the stack.
func stack_at(stack: Node*, n: felt) -> (value: felt) {
    if (n == 0) {
        // Add your code here.
    }

    // Add your code here.
}

func main() -> () {
    alloc_locals;
    // Start with an empty stack.
    let (stack) = empty_stack();
    // Push 1, 10, 100.
    let (stack) = push(stack, 1);
    let (stack) = push(stack, 10);
    let (local stack) = push(stack, 100);

    // Check the size of the stack.
    assert stack.size = 3;

    // Query the stack at indices 0, 1 and 2.
    let (value) = stack_at(stack, 0);
    assert value = 100;
    let (value) = stack_at(stack, 1);
    assert value = 10;
    let (value) = stack_at(stack, 2);
    assert value = 1;

    // Pop the top 2 values (100 and 10) and push 1000.
    let (stack, value) = pop(stack);
    assert value = 100;
    let (stack, value) = pop(stack);
    assert value = 10;
    let (local stack) = push(stack, 1000);

    // Query the stack at indices 0 and 1.
    let (value) = stack_at(stack, 0);
    assert value = 1000;
    let (value) = stack_at(stack, 1);
    assert value = 1;

    return ();
}
```

---

> Answers to this question are a part of the ✨ 17 days of Cairo Lang with Playground & Newton. ✨
> 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*

How to create Structs in Cairo Lang for StarkNet?

How do I create OZ (Open Zeppelin) contract using starknetjs?

I'm looking for a StarkNet guide. I'm an experienced CTO and I want to know more about it, check out, and learn more. Also want to get hyped. What can you recommend to read to learn more about StarkNet?

What's the best advanced StarkNet guide?

gm all! I am working on this project https://github.com/outsider-analytics/ZK-Circuit-Performance-and-Security-Data on a grant from the EF PSE team.  I need to understand what hash types are being used in the STARK proof creations.  I have poured through the docs and can't seem to find it.  I have seen reference to Pedersen and Rescue, but can't find anything definitive.  Can someone point me towards any documentation that can help me?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Can anyone point me to Pedersen, Rescue references? StarkNet / Cairo Lang

Python issues with Pathfinder

Does AA work on Mobile?

---

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