How to map db.QueryRow.Scan results into map in Go language?
Apr 02, 2025 am 11:21 AM
Go language database operation: cleverly map db.QueryRow.Scan results to map
In Go database operations, it is common to map query results to custom structures. However, sometimes it is necessary to map the results into map . This article will explain in detail how to scan the results of db.QueryRow.Scan into map[string]interface{} and resolve common errors.
It is wrong to use map[string]interface{} directly as Scan parameter, because Scan function requires a pointer to write data. The following code snippet shows common errors:
res := map[string]interface{}{"id": nil, "name": nil, "password": nil, "add_time": nil}
// ... Scan(res["id"], res["name"], ...) // Error!
res["id"] , etc. return a value of type interface{} , not a pointer. Scan function cannot write data to these values.
The correct way to do this is to allocate memory space for each map value and use pointers:
res := map[string]interface{}{"id": new(int), "name": new(string), "password": new(string), "add_time": new(int64)}
Here, use the new() function to allocate memory for int , string and int64 types respectively, and get their pointers. Scan function can write data to the memory address pointed to by these pointers.
The improved selectOne function is as follows:
func selectOne(id int) {
res := map[string]interface{}{"id": new(int), "name": new(string), "password": new(string), "add_time": new(int64)}
fmt.Println("Initial map:", res) // Add print statements to facilitate debugging of sql := "select id, name, password, add_time from test where id = ?"
err := db.QueryRow(sql, id).Scan(res["id"], res["name"], res["password"], res["add_time"])
if err != nil {
fmt.Println("Failed to get data:", err.Error())
} else {
fmt.Println("Result map:", res) // Add print statements to facilitate debugging // Access data in map idVal := *res["id"].(*int)
nameVal := *res["name"].(*string)
// ...
}
}
Note that accessing data in map requires type assertions, such as *res["id"].(*int) . This ensures that interface{} is converted to int type correctly. We have also added print statements to facilitate debugging and understanding data flow. The SQL statement has also been adjusted to specify the column names to be queried to avoid potential column name mismatch problems. Remember that the key name of map must be consistent with the database column name.
With this approach, the results of db.QueryRow.Scan can be mapped to map effectively and avoid common pointer errors. Remember to always allocate memory for the values ??in map and use pointers.
The above is the detailed content of How to map db.QueryRow.Scan results into map in Go language?. For more information, please follow other related articles on the PHP Chinese website!
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