TheLazy.Dev
Portfolio GitHub

Blog

picolisp |lisp |database |webdev

How to Add Records to the PicoLisp Database

miatemma

Mia

Posted on March 18, 2022

How to Add Records to the PicoLisp Database

In the last post, we have created a simple entity/relation-model using the PicoLisp E/R framework. You can find the file with the definitions here.

Now let's create a new database and fill it with some values.

Create a new database

First of all, let's start the file from the REPL and open a new database file.

$ pil family-dbmodel.l +

: (pool "myFamily.db")
-> T
Enter fullscreen mode Exit fullscreen mode

The database is empty:

: (show *DB)
{1} NIL
-> {1}
Enter fullscreen mode Exit fullscreen mode

Inserting some data using the request function

From the previous posts you might remember that we can insert new items with the new function. However, for many cases there is a better alternative: the request function. What's the difference? request returns an object from the database if it exists, otherwise it creates a new one. This avoids that duplicates are inserted by mistake.

Syntax and example from the documentation:

(request 'typ 'sym ['hook] 'val ..) -> obj

Example:

: (request '(+Item) 'nr 2)
-> {B2}

Let's create an object of the class +Man called Adam.

: (request '(+Man) 'name "Adam")
-> {2}
Enter fullscreen mode Exit fullscreen mode

This seems to have worked. Let's insert Eve as well.

: (request '(+Woman) 'name "Eve")
-> {6}
Enter fullscreen mode Exit fullscreen mode

Querying the data

Let's see what we have in our database now:

: (show *DB)
{1} NIL
   +Person {3}
   +Woman {7}
   +Man {4}
-> {1}
Enter fullscreen mode Exit fullscreen mode

Well, it's not empty anymore, but we don't see anything like "Adam" or "Eve", only the object class names. In order to find our entries, we need to query the database. One of the most useful functions for that is collect.

collect has several options, for now let's only consider the most easy one: return all objects of a certain class. Again from the documentation:

(collect 'sym 'cls (...) )

Returns a list of all database objects of class cls, where the values for the sym arguments correspond to the any arguments (...)

: (collect 'nr '+Item)
-> ({B1} {B2} {B3} {B4} {B5} {B6} {B8})

So, applied to our example: We know we have inserted one +Woman and one +Man, both of them are +Person. We can query it like this:

: (collect 'name '+Person)
-> ({2} {6})
Enter fullscreen mode Exit fullscreen mode

This looks better! We can confirm that we have the right return values with show:

: (show '{2})
{2} (+Man)
   name "Adam"
-> {2}
Enter fullscreen mode Exit fullscreen mode

However it would be nice to receive this directly in one query. For this we can use the more function, which accepts a list and a function as arguments.

(more 'lst ['fun]) -> flg

Displays the elements of lst (first form). After each step, more waits for console input, and terminates when a non-empty line is entered. In that case, T is returned, otherwise (when end of data is reached) NIL.

Applied to our example:

: (more (collect 'name '+Person) show)
{2} (+Man)
   name "Adam"

{6} (+Woman)
   name "Eve"
Enter fullscreen mode Exit fullscreen mode

Let's commit the content up to now to the database by commit:

: (commit)
T
Enter fullscreen mode Exit fullscreen mode

Defining the relationships

What other fields do we have? About Adam and Eve we don't have much information about birthday, death day and job. But we can define the relationship between them.

Adam and Eve are partners. Since the partner attribute is a +Joint connection, it's enough to define it on one side to automatically set it on the other side as well. We can set the relation using the function put> and (commit). As a shortcut, we could also do put!> in one step.

Note: put> is a method of the +Entity class and should not be confused with put for "normal" objects.

Since we know that Adam is {2} and Eve is {6}, we can address them directly. This is OK for debugging mode - in a real application, it should't be addressed directly because it could corrupt the debugger.

So, we set Eve as partner of Adam:

: (put!> '{2} 'partner '{6})
-> {6}
Enter fullscreen mode Exit fullscreen mode

Let's check both of them: They should now be partners of each other.

: (show '{2})
{2} (+Man)
   partner {6}
   name "Adam"
-> {2}

: (show '{6})
{6} (+Woman)
   partner {2}
   name "Eve"
-> {6}
Enter fullscreen mode Exit fullscreen mode

Some more entries

Let's also add the children: Kain, Abel and Set. We can add their jobs and parents as well.

: (request '(+Man) 'name "Kain" 'job "farmer" 'father '{2} 'mother '{6})
-> {12}
: (request '(+Man) 'name "Abel" 'job "shepherd" 'father '{2} 'mother '{6})
-> {14}
: (request '(+Man) 'name "Seth" 'father '{2} 'mother '{6})
-> {15}

: (commit)
-> T
Enter fullscreen mode Exit fullscreen mode

Now both Adam and Eve have another attribute "kids" which contains three items:

: (show '{2})
{2} (+Man)
   kids ({15} {14} {12})
   partner {6}
   name "Adam"
-> {2}
Enter fullscreen mode Exit fullscreen mode

Again, we could step through Adam's kids using a combination of more and show. Instead of show we could also use get:

: (more (get '{2} 'kids) show)
{15} (+Man)
   mother {6}
   father {2}
   name "Seth"

{14} (+Man)
   mother {6}
   father {2}
   job "shepherd"
   name "Abel"

{12} (+Man)
   mother {6}
   father {2}
   job "farmer"
   name "Kain"
Enter fullscreen mode Exit fullscreen mode

Validation checks

As you might remember, for some values we have defined the types. For example, the birthday needs to be of class +Date:

(rel birthday (+Ref +Date))
Enter fullscreen mode Exit fullscreen mode

Let's see what happens if we define a string instead.

: (put> '{2} 'birthday "Genesis")
-> "Genesis"
Enter fullscreen mode Exit fullscreen mode

Well, it seems it was accepted although "Genesis" is clearly not a date type.

: (show '{2})
{2} (+Man)
   birthday "Genesis"
   kids ({15} {14} {12})
   partner {6}
   name "Adam"
-> {2}
Enter fullscreen mode Exit fullscreen mode

However, we can check if the data is correct using the mis> function.

: (mis> '{2} 'birthday "Genesis")
-> "Numeric input expected"
Enter fullscreen mode Exit fullscreen mode

Therefore you should always run mis> before you commit any input into a database, for consistency and also for security reasons.

In the next post we will expand this little example to a larger database which already has some values inside.

Sources

💖 💪 🙅 🚩
miatemma
Mia

Posted on March 18, 2022

Join Our Newsletter. No Spam, Only the good stuff.

Sign up to receive the latest update from our blog.

Related

How to Add Records to the PicoLisp Database
picolisp How to Add Records to the PicoLisp Database

March 18, 2022