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Advanced parameters
Advanced params usage
Sometimes you may need to use multiple parameters for a module. To pass multiple parameters, you can encode them as a URL-encoded query string, i.e.
param1=value1¶m2=value2.Suppose you want to track transfers to/from a certain address exceeding a certain amount of ETH. Your module manifest could look like this:
modules:
- name: map_whale_transfers
kind: map
inputs:
- params: string
- source: sf.ethereum.type.v2.Block
output:
type: proto:Transfers
params:
map_params: address=aaa..aaa&amount=100
Our module gets a params string with two parameters:
address and amount.In your module handler, you can decode your parameters using one of the URL decoding crates such as
serde_qs, serde_urlencoded or your own helper functions. Here's an example using serde_qs:#[derive(Debug, Deserialize)]
struct Params {
address: String,
amount: u64,
}
#[substreams::handlers::map]
pub fn map_whale_transfers(params: String, block: Block) -> Result<Transfers, Error> {
let query: Params = serde_qs::from_str(params.as_str()).unwrap();
log::info!("Tracking transfers for address: {} of more than {} ETH", query.address, query.amount);
// filter transfers by address and amount
}
Sometimes parameters can be optional, i.e. you want to track all transfers rather than a specific address. Decoding will look like this in that case:
#[derive(Debug, Deserialize)]
struct QueryParams {
address: Option<String>,
amount: u64,
}
#[substreams::handlers::map]
pub fn map_whale_transfers(params: String, block: Block) -> Result<Transfers, Error> {
let query: QueryParams = serde_qs::from_str(params.as_str()).unwrap();
if query.address.is_none() {
log::info!("Tracking all of more than {} ETH", query.amount);
}
else {
log::info!("Tracking transfers for address: {} of more than {} ETH", query.address, query.amount);
}
}
You can even pass a vector of addresses to track multiple specific whales in our example:
#[derive(Debug, Deserialize)]
struct QueryParams {
address: Vec<String>,
amount: u64,
}
#[substreams::handlers::map]
pub fn map_whale_transfers(params: String, block: Block) -> Result<Transfers, Error> {
let query: QueryParams = serde_qs::from_str(params.as_str()).unwrap();
log::info!("Tracking transfers for addresses: {:?} of more than {} ETH", query.address, query.amount);
}
Depending on the crate you use to decode params string, you can pass them to Substreams CLI like this for example:
substreams gui map_whale_transfers -p map_whale_transfers="address[]=aaa..aaa&address[]=bbb..bbb&amount=100"
Last modified 2mo ago