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cassandra.ts
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cassandra.ts
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import { Client, DseClientOptions } from "cassandra-driver";
import {
BaseMessage,
BaseListChatMessageHistory,
StoredMessage,
} from "../../schema/index.js";
import {
mapChatMessagesToStoredMessages,
mapStoredMessagesToChatMessages,
} from "./utils.js";
export interface CassandraChatMessageHistoryOptions extends DseClientOptions {
keyspace: string;
table: string;
sessionId: string;
}
/**
* Class for storing chat message history within Cassandra. It extends the
* BaseListChatMessageHistory class and provides methods to get, add, and
* clear messages.
*/
export class CassandraChatMessageHistory extends BaseListChatMessageHistory {
lc_namespace = ["langchain", "stores", "message", "cassandra"];
private keyspace: string;
private table: string;
private client: Client;
private sessionId: string;
private tableExists: boolean;
private options: CassandraChatMessageHistoryOptions;
private queries: { insert: string; select: string; delete: string };
constructor(options: CassandraChatMessageHistoryOptions) {
super();
this.client = new Client(options);
this.keyspace = options.keyspace;
this.table = options.table;
this.sessionId = options.sessionId;
this.tableExists = false;
this.options = options;
}
/**
* Method to get all the messages stored in the Cassandra database.
* @returns Array of stored BaseMessage instances.
*/
public async getMessages(): Promise<BaseMessage[]> {
await this.ensureTable();
const resultSet = await this.client.execute(
this.queries.select,
[this.sessionId],
{ prepare: true }
);
const storedMessages: StoredMessage[] = resultSet.rows.map((row) => ({
type: row.message_type,
data: JSON.parse(row.data),
}));
const baseMessages = mapStoredMessagesToChatMessages(storedMessages);
return baseMessages;
}
/**
* Method to add a new message to the Cassandra database.
* @param message The BaseMessage instance to add.
* @returns A promise that resolves when the message has been added.
*/
public async addMessage(message: BaseMessage): Promise<void> {
await this.ensureTable();
const messages = mapChatMessagesToStoredMessages([message]);
const { type, data } = messages[0];
return this.client
.execute(
this.queries.insert,
[this.sessionId, type, JSON.stringify(data)],
{ prepare: true, ...this.options }
)
.then(() => {});
}
/**
* Method to clear all the messages from the Cassandra database.
* @returns A promise that resolves when all messages have been cleared.
*/
public async clear(): Promise<void> {
await this.ensureTable();
return this.client
.execute(this.queries.delete, [this.sessionId], {
prepare: true,
...this.options,
})
.then(() => {});
}
/**
* Method to initialize the Cassandra database.
* @returns Promise that resolves when the database has been initialized.
*/
private async ensureTable(): Promise<void> {
if (this.tableExists) {
return;
}
await this.client.execute(`
CREATE TABLE IF NOT EXISTS ${this.keyspace}.${this.table} (
session_id text,
message_ts timestamp,
message_type text,
data text,
PRIMARY KEY ((session_id), message_ts)
);
`);
this.queries = {
insert: `INSERT INTO ${this.keyspace}.${this.table} (session_id, message_ts, message_type, data) VALUES (?, toTimestamp(now()), ?, ?);`,
select: `SELECT message_type, data FROM ${this.keyspace}.${this.table} WHERE session_id = ?;`,
delete: `DELETE FROM ${this.keyspace}.${this.table} WHERE session_id = ?;`,
};
this.tableExists = true;
}
}