如何进行数据库查询，然后检查结果

Question

I need to check if my query returns true or false. If it returns false, I want it to error out. Here is my code:

func (dr *dbrepo) checkIfUnique(datacenterstring) error {
    statement := `select exists(select 1 from source where datacenter = $3)`

    _, checkIfExists := dr.db.Query(statement)
    if checkIfExists != nil {
        log.Print("Error  is not unique", checkIfExists)
        return checkIfExists
    }
    return nil
}

The problem is: I think I need to convert checkIfExists from a row to a bool and then see if it is true or false. But I am not sure on how to do that. Any ideas? Is there a better way to do this?

Answer 1

Query() does not return true or false. It returns two values: *Rows & error.

func (db *DB) Query(query string, args ...interface{}) (*Rows, error) {
    ...
}

In your case: checkIfExists is the error. With this error, you can already tell of the query succeeded or failed. Like you do it:

if checkIfExists != nil {
    return checkIfExists
}

If you want more information (such as the rows retrieved by your query), then you will need to replace the _ with a variable. Let's call it rows and then you use rows.Scan() to copy the data in the columns to your destinations. See database/sql docs for more information.