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Normalizing a database interface

From: Python 3 Essential Training

Video: Normalizing a database interface

As you build applications in Python, you are probably going to find that you use databases quite a bit and so you will probably find some value in having a normalized interface for working with your databases. I have built such a normalized interface and you are welcome to use mine but I would suggest that you simply use this as a model and build your own. Build one that works for you, that works for the way that you like to work with databases. So I will show you mine as an example. It's called bwDB.py and it's in the lib folder, in the 19 Projects folder in your Exercise Files. So go ahead and open that up and we will maximize this so that we can take a look.

Normalizing a database interface

As you build applications in Python, you are probably going to find that you use databases quite a bit and so you will probably find some value in having a normalized interface for working with your databases. I have built such a normalized interface and you are welcome to use mine but I would suggest that you simply use this as a model and build your own. Build one that works for you, that works for the way that you like to work with databases. So I will show you mine as an example. It's called bwDB.py and it's in the lib folder, in the 19 Projects folder in your Exercise Files. So go ahead and open that up and we will maximize this so that we can take a look.

Of course it imports SQLite3. This is a library for using SQLite3, like I said. For most of my web applications these days I am using SQLite3, because it's small, it's fast, it's self-contained, it's easy and it's very robust and reliable. I've never had any problems with it. So there is a class here called bwDB and the first thing in it is the constructor, and the constructor simply takes this keyword arguments and it looks for the file name and the table name.

You will notice that in each of these methods I have what's called a docstring. If the first line in a function or a method is just a string by itself this is picked up by Python's documentation protocol and it's called a docstring. I use it to describe how the function works. So this is the constructor method, the table is for the CRUD methods and you don't have to use that. I will get to that in a moment. And the file name is for connecting to the database file.

Here is one of my workhorse methods. It's called sql_do. This is for non-selective type queries. You just pass it in some SQL, you pass it in some parameters, and it does its job. This next one, sql_query, is the same thing except that it also works as a generator and it will iterate through set of results, and of course each result is a row factory. You will notice that the constructor assigns file name here and file name is actually a property, which is defined down below, and we have seen this technique already. And so in the setter when a file name gets assigned it sets the attribute in the object.

It also connects to the database and it sets up the row query. So this is actually a constructor of sorts but it allows you to change files if you want to. If you are using the object and you decide that you need to assign this object to a different database file, first of course, it will call the Destructor which closes the old database, and then it'll call this constructor for the file name and it will connect to the new database. This works really, really well.

We have and sql_query method for returning a single row, and we have an sql_query method for returning a single value. I find these very useful and I use them a lot. Again depending on how your pattern of dealing with database is, you might find different things useful and I would suggest that you use those. Now we get into the CRUD methods. CRUD stands for create, retrieve, update and delete. These are the basic four functions of a database. So this is the getrec that just would be the retrieve part of CRUD, and for my CRUD methods I depend on their being a column in the table that's called id.

So all of my tables and all of my applications that are going to use these methods must have a column called id. I typically create this column in SQLite using the integer primary key feature which makes that column an equivalent for SQLite's internal row id. This all just works very nicely together and you will see examples of this in the projects that we are going to look at in this chapter. Getrecs is a method that returns all of the rows in the table and it returns it as a generator with row factories.

Insert inserts a record and this uses a dictionary for the record. This is actually very interesting. This method constructs the SQL based on the names of the keys in the dictionary object that gets passed. So it takes a little bit of care to work with it but when you use it with care it works very, very well. This next method works the same way. Again it constructs the sql_query based on the keys in the dictionary object that gets passed and this will update a particular record based on an id that's passed.

Finally we have the delete method where it deletes based on the id, deletes the row from the table based on the id and a countrecs method that simply gives us a count of all the records in the table. This is a very fast operation to do in SQL. Most database engines including SQLite are very highly optimized for count operations. So this method offloads that work to the database engine and allows it to happen very quickly.

Finally we have the property accessors for the filename property and a close method for closing the database. Then we have a test method for testing and we will go ahead and run that. And that creates a database in memory. Sqlite has a feature where if you give the filename as this with colons on either side of it, that whole thing is the filename then it will create a database in memory. Creates a table, inserts into the table, reads from the table, updates a table.

Exercises all of the CRUD methods. So that is my example of a normalized database interface. I find this very useful and you'll see an example of it here in this chapter of how I use this. It makes it that much easier for me to work with databases in my applications, and these days in the little web applications that I might be working on it saves me a lot of time in work and allows me to focus on the logic of the code.

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This video is part of

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Python 3 Essential Training

87 video lessons · 38438 viewers

Bill Weinman
Author

 
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  1. 5m 14s
    1. Welcome
      1m 32s
    2. Understanding prerequisites for Python
      2m 4s
    3. Using the exercise files
      1m 38s
  2. 33m 29s
    1. Getting started with "Hello World"
      4m 43s
    2. Selecting code with conditionals
      4m 45s
    3. Repeating code with a loop
      4m 13s
    4. Reusing code with a function
      2m 43s
    5. Creating sequences with generator functions
      2m 46s
    6. Reusing code and data with a class
      4m 39s
    7. Greater reusability with inheritance and polymorphism
      7m 17s
    8. Handling errors with exceptions
      2m 23s
  3. 22m 32s
    1. Installing Python 3 and Eclipse for Windows
      11m 24s
    2. Installing Python 3 and Eclipse for Mac
      11m 8s
  4. 28m 0s
    1. Creating a main script
      3m 27s
    2. Understanding whitespace in Python
      4m 8s
    3. Commenting code
      3m 28s
    4. Assigning values
      3m 37s
    5. Selecting code and values with conditionals
      4m 46s
    6. Creating and using functions
      3m 54s
    7. Creating and using objects
      4m 40s
  5. 31m 23s
    1. Understanding variables and objects in Python
      2m 46s
    2. Distinguishing mutable and immutable objects
      2m 41s
    3. Using numbers
      3m 34s
    4. Using strings
      6m 38s
    5. Aggregating values with lists and tuples
      4m 55s
    6. Creating associative lists with dictionaries
      4m 24s
    7. Finding the type and identity of a variable
      4m 45s
    8. Specifying logical values with True and False
      1m 40s
  6. 9m 42s
    1. Selecting code with if and else conditional statements
      2m 22s
    2. Setting multiple choices with elif
      2m 14s
    3. Understanding other strategies for multiple choices
      2m 38s
    4. Using the conditional expression
      2m 28s
  7. 11m 26s
    1. Creating loops with while
      1m 27s
    2. Iterating with for
      3m 54s
    3. Enumerating iterators
      3m 22s
    4. Controlling loop flow with break, continue, and else
      2m 43s
  8. 23m 28s
    1. Performing simple arithmetic
      2m 14s
    2. Operating on bitwise values
      3m 30s
    3. Comparing values
      3m 32s
    4. Operating on Boolean values
      2m 59s
    5. Operating on parts of a container with the slice operator
      6m 52s
    6. Understanding operator precedence
      4m 21s
  9. 11m 34s
    1. Using the re module
      1m 4s
    2. Searching with regular expressions
      3m 12s
    3. Replacing with regular expressions
      3m 29s
    4. Reusing regular expressions with re.compile
      3m 49s
  10. 9m 10s
    1. Learning how exceptions work
      1m 18s
    2. Handling exceptions
      4m 15s
    3. Raising exceptions
      3m 37s
  11. 23m 1s
    1. Defining functions
      6m 23s
    2. Using lists of arguments
      2m 26s
    3. Using named function arguments
      4m 32s
    4. Returning values from functions
      1m 55s
    5. Creating a sequence with a generator function
      7m 45s
  12. 47m 29s
    1. Understanding classes and objects
      5m 12s
    2. Using methods
      6m 12s
    3. Using object data
      10m 4s
    4. Understanding inheritance
      5m 11s
    5. Applying polymorphism to classes
      7m 13s
    6. Using generators
      9m 48s
    7. Using decorators
      3m 49s
  13. 18m 54s
    1. Understanding strings as objects
      3m 25s
    2. Working with common string methods
      5m 24s
    3. Formatting strings with str.format
      5m 31s
    4. Splitting and joining strings
      2m 49s
    5. Finding and using standard string methods
      1m 45s
  14. 25m 27s
    1. Creating sequences with tuples and lists
      4m 6s
    2. Operating on sequences with built-in methods
      5m 50s
    3. Organizing data with dictionaries
      4m 56s
    4. Operating on character data with bytes and byte arrays
      10m 35s
  15. 11m 46s
    1. Opening files
      2m 4s
    2. Reading and writing text files
      4m 33s
    3. Reading and writing binary files
      5m 9s
  16. 21m 27s
    1. Creating a database with SQLite 3
      6m 56s
    2. Creating, retrieving, updating, and deleting records
      7m 31s
    3. Creating a database object
      7m 0s
  17. 18m 27s
    1. Using standard library modules
      8m 0s
    2. Finding third-party modules
      5m 47s
    3. Creating a module
      4m 40s
  18. 23m 11s
    1. Dealing with syntax errors
      8m 19s
    2. Dealing with runtime errors
      4m 0s
    3. Dealing with logical errors
      4m 22s
    4. Using unit tests
      6m 30s
  19. 19m 56s
    1. Normalizing a database interface
      6m 39s
    2. Deconstructing a database application
      8m 9s
    3. Displaying random entries from a database
      5m 8s
  20. 29s
    1. Goodbye
      29s

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