增量查数据库

Posted 2023-03-29 让速不让路

Person:

• I hope that I can incrementally query the database to obtain data. I will store the results of each database query in redis and record the time a of this query. Next time I query the database, I will only check the data with lastEditedDate>=a and get The data in redis is returned after merging the two. (The method signature can be listed, no implementation code is required)

ChatGPT:

• Sure, here\'s an example of a method that retrieves data from a database using incremental querying and caches the results in Redis:

import (
    "context"
    "fmt"
    "time"

    "github.com/go-redis/redis/v8"
    "database/sql"
)

// QueryDatabase queries the database and caches the results in Redis.
func QueryDatabase(db *sql.DB, redisClient *redis.Client, query string, user string, since time.Time) ([]string, error) 
    // Define the Redis key for the cached query results.
    key := fmt.Sprintf("%s:%s", user, query)

    // Check if the results are already cached in Redis.
    cachedResults, err := redisClient.ZRangeByScore(context.Background(), key, &redis.ZRangeBy
        Min: fmt.Sprintf("%d", since.Unix()),
        Max: "+inf",
    ).Result()
    if err != nil && err != redis.Nil 
        return nil, err
    

    // If the results are already cached, return them.
    if len(cachedResults) > 0 
        return cachedResults, nil
    

    // If the results are not cached, query the database and cache the results in Redis.
    rows, err := db.Query(query)
    if err != nil 
        return nil, err
    

    // Iterate over the database rows and store the results in Redis.
    for rows.Next() 
        var result string
        err = rows.Scan(&result)
        if err != nil 
            return nil, err
        

        // Cache the result in Redis with the current time as the score.
        _, err = redisClient.ZAdd(context.Background(), key, &redis.Z
            Score:  float64(time.Now().Unix()),
            Member: result,
        ).Result()
        if err != nil 
            return nil, err
        
    

    // Set an expiration time for the cached results.
    _, err = redisClient.Expire(context.Background(), key, time.Hour).Result()
    if err != nil 
        return nil, err
    

    // Retrieve the cached results from Redis.
    cachedResults, err = redisClient.ZRangeByScore(context.Background(), key, &redis.ZRangeBy
        Min: fmt.Sprintf("%d", since.Unix()),
        Max: "+inf",
    ).Result()
    if err != nil 
        return nil, err
    

    // Return the cached results.
    return cachedResults, nil

This method takes as input a database connection (*sql.DB), a Redis client (*redis.Client), a SQL query string (query), the current user (user), and a timestamp indicating the last time the data was queried (since).

The method first checks if the results of the query are already cached in Redis using the specified key format (user:query). If the results are already cached and have been queried since the last time the data was queried, they are returned directly from Redis.

If the results are not already cached, the method queries the database using the specified SQL query string, iterates over the database rows, and caches each result in Redis with the current time as the score.

Finally, the method sets an expiration time for the cached results and retrieves the cached results from Redis using the specified key and timestamp.

Note that this method assumes that the database and Redis are already set up and running. It also assumes that the SQL query string is properly formatted and that the query returns a single column of strings.

You can call this method from your application code to query the database incrementally and cache the results in Redis.