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119 lines
3.7 KiB
Markdown
119 lines
3.7 KiB
Markdown
---
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order: 6
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---
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# Indexing Transactions
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Tendermint allows you to index transactions and later query or subscribe
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to their results.
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Events can be used to index transactions and blocks according to what happened
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during their execution. Note that the set of events returned for a block from
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`BeginBlock` and `EndBlock` are merged. In case both methods return the same
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tag, only the value defined in `EndBlock` is used.
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Each event contains a type and a list of attributes, which are key-value pairs
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denoting something about what happened during the method's execution. For more
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details on `Events`, see the [ABCI](../spec/abci/abci.md) documentation.
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Let's take a look at the `[tx_index]` config section:
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```toml
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##### transactions indexer configuration options #####
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[tx_index]
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# What indexer to use for transactions
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#
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# Options:
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# 1) "null"
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# 2) "kv" (default) - the simplest possible indexer, backed by key-value storage (defaults to levelDB; see DBBackend).
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indexer = "kv"
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# Comma-separated list of tags to index (by default the only tag is "tx.hash")
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#
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# You can also index transactions by height by adding "tx.height" tag here.
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#
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# It's recommended to index only a subset of tags due to possible memory
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# bloat. This is, of course, depends on the indexer's DB and the volume of
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# transactions.
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index_tags = ""
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# When set to true, tells indexer to index all tags (predefined tags:
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# "tx.hash", "tx.height" and all tags from DeliverTx responses).
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#
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# Note this may be not desirable (see the comment above). IndexTags has a
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# precedence over IndexAllTags (i.e. when given both, IndexTags will be
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# indexed).
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index_all_tags = false
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```
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By default, Tendermint will index all transactions by their respective
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hashes using an embedded simple indexer. Note, we are planning to add
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more options in the future (e.g., PostgreSQL indexer).
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## Adding Events
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In your application's `DeliverTx` method, add the `Events` field with pairs of
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UTF-8 encoded strings (e.g. "transfer.sender": "Bob", "transfer.recipient": "Alice",
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"transfer.balance": "100").
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Example:
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```go
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func (app *KVStoreApplication) DeliverTx(req types.RequestDeliverTx) types.Result {
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//...
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events := []abci.Event{
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{
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Type: "transfer",
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Attributes: cmn.KVPairs{
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cmn.KVPair{Key: []byte("sender"), Value: []byte("Bob")},
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cmn.KVPair{Key: []byte("recipient"), Value: []byte("Alice")},
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cmn.KVPair{Key: []byte("balance"), Value: []byte("100")},
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},
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},
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}
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return types.ResponseDeliverTx{Code: code.CodeTypeOK, Events: events}
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}
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```
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If you want Tendermint to only index transactions by "transfer.sender" event type,
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in the config set `tx_index.index_tags="transfer.sender"`. If you to index all events,
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set `index_all_tags=true`
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Note, there are a few predefined event types:
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- `tx.hash` (transaction's hash)
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- `tx.height` (height of the block transaction was committed in)
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Tendermint will throw a warning if you try to use any of the above keys.
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## Querying Transactions
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You can query the transaction results by calling `/tx_search` RPC endpoint:
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```shell
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curl "localhost:26657/tx_search?query=\"account.name='igor'\"&prove=true"
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```
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Check out [API docs](https://tendermint.com/rpc/#txsearch) for more information
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on query syntax and other options.
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## Subscribing to Transactions
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Clients can subscribe to transactions with the given tags via Websocket by providing
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a query to `/subscribe` RPC endpoint.
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```json
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{
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"jsonrpc": "2.0",
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"method": "subscribe",
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"id": "0",
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"params": {
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"query": "account.name='igor'"
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}
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}
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```
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Check out [API docs](https://tendermint.com/rpc/#subscribe) for more information
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on query syntax and other options.
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