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Creating an instance of a class from a result set

From: Accessing Databases with Object-Oriented PHP

Video: Creating an instance of a class from a result set

With MySQL Improved, you can create an instance of a custom The class uses the magic set and get methods to set and get To instantiate a custom object from the database result, the So let's create our custom object, we'll call it car.

Creating an instance of a class from a result set

With MySQL Improved, you can create an instance of a custom class and initialize the object's properties with values from a database result. However, you need to be aware that MySQLi sets the objects properties before calling the class's constructor method. The following example shows how it works. This is car.ID, which you can find in the ch07 > 07_05 folder of the exercise files, along with the other files that will be used in this video.

Car.php contains the definition for a custom PHP class called car. The Constructor method takes a single argument, the car's ID, which is then used to set the car ID property. Four other properties are set to default values in the constructor. The class uses the magic set and get methods to set and get the values of properties that don't have their own setter and getter methods. And down at the bottom, the definition of the magic toString returns HTML that displays the objects properties and their values.

So let's use this to create an instance of the car class. Open mysqli_class.php. This contains the database connection and the definition of the car class. Then it fetches the details of a car using its ID and stores the result as result. To instantiate a custom object from the database result, the result set must be stored as a MySQLi result object. That's why I've used the query method here.

So let's create our custom object, we'll call it car. Then we use the result object and we call it fetch_object_ method. And the first argument to fetch object is a string which is the name of the custom class. The second argument, which is optional, is an array of arguments to be passed to the constructor. In this case, we've got only one argument that needs to be passed. So, we have an array with a single element in it, which is car_ID. The class is magic to string method.

Displays all of the object properties and values so we can use echo to inspect our new object. And if we save that page and load it into a browser. We get the correct car ID but make is unknown, mileage is not registered. And this is the problem with the fetch object method. MySQLi uses the values drawn from the database to set the object's properties and then calls the constructor. As a result, the default values in the constructor overwrite the values from the database, and there's nothing you can do about it other than get rid of default values.

So, if we go back to our code, and to the car definition. Scroll up to the constructor. If we comment out these default properties, and save that page, then go back to the browser and reload. The values from the database are used to populate the property values. Unfortunately, there's currently no way to get the fetch object method to call the constructor first. So, if you're working with objects that have default values in the constructor, you should use PDO as described in chapter 4 rather than MySQLi.

The fetch object method works only with a my SQLI result object. If you're working with a prepared statement, let's just take a little quick look at that. Mysqli_class_stmp.php. This uses a prepared statement. Then on line 18, the get_result method is used to store the result as a MySQLi result object. The fetch object method won't work directly on a statement. So that's how you create a custom object and set it's properties using a database result with MySQLi.

The main limitation is that the fetch object method calls the class constructor after setting the values. As a result, any default values overwrite those drawn from the database.

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This video is part of

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Accessing Databases with Object-Oriented PHP

47 video lessons · 1875 viewers

David Powers
Author

 
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  1. 13m 33s
    1. Welcome
      1m 4s
    2. What you should know before watching this course
      2m 8s
    3. Using the exercise files
      4m 56s
    4. Setting SQLite permissions
      1m 11s
    5. A quick primer on using PHP objects
      4m 14s
  2. 10m 12s
    1. Overview of PHP database APIs
      4m 5s
    2. Using prepared statements
      4m 24s
    3. Using transactions
      1m 43s
  3. 48m 57s
    1. Creating a database source name
      2m 3s
    2. Connecting to a database with PDO
      7m 27s
    3. Looping directly over a SELECT query
      3m 49s
    4. Fetching a result set
      8m 3s
    5. Finding the number of results from a SELECT query
      7m 14s
    6. Checking if a SELECT query contains results
      3m 32s
    7. Executing simple non-SELECT queries
      6m 2s
    8. Getting error messages
      7m 17s
    9. Using the quote() method to sanitize user input
      3m 30s
  4. 39m 51s
    1. Binding input and output values
      2m 36s
    2. Using named parameters
      9m 51s
    3. Using question marks as anonymous placeholders
      2m 35s
    4. Passing an array of values to the execute() method
      5m 20s
    5. Binding results to variables
      7m 53s
    6. Executing a transaction
      6m 54s
    7. Closing the cursor before running another query
      4m 42s
  5. 21m 20s
    1. Generating an array from a pair of columns
      2m 44s
    2. Setting an existing object's properties with a database result
      4m 42s
    3. Creating an instance of a specific class with a database result
      6m 1s
    4. Reusing a result set
      7m 53s
  6. 38m 14s
    1. Connecting to a database with MySQLi
      5m 57s
    2. Setting the character set
      1m 57s
    3. Submitting a SELECT query and getting the number of results
      4m 4s
    4. Fetching the result
      7m 35s
    5. Rewinding the result for reuse
      3m 20s
    6. Handling non-SELECT queries
      5m 27s
    7. Getting error messages
      5m 47s
    8. Sanitizing user input with real_escape_string()
      4m 7s
  7. 27m 49s
    1. Initializing and preparing a statement
      4m 17s
    2. Binding parameters and executing a prepared statement
      5m 55s
    3. Binding output variables
      5m 6s
    4. Executing a MySQLi transaction
      7m 5s
    5. Dealing with "commands out of sync" in prepared statements
      5m 26s
  8. 24m 7s
    1. Buffered and unbuffered queries
      4m 19s
    2. Using real_query()
      6m 1s
    3. Freeing resources that are no longer needed
      2m 31s
    4. Submitting multiple queries
      6m 41s
    5. Creating an instance of a class from a result set
      4m 35s
  9. 3m 31s
    1. PDO and MySQLi compared
      3m 31s

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