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A python library for postgresql focused on performance and supporting ORM and query-building functionality

Project description

ichorORM

A python library for postgresql focused on performance and supporting ORM and query-building functionality. It supports transactions and autocommit mode.

ichorORM uses psycopg2 to interact with a configured SQL database and provides an easy and efficient abstraction layer.

The default mode handles SQL parameterization to automatically protect against SQL-injection attacks.

Connecting to the Database

ichorORM provides two means of connection to the database.

Global Connection

The first is the “global” connection info. This is the default used for everything unless specified otherwise.

Set these fields via the setGlobalConnectionParams method

setGlobalConnectionParams(host=’localhost’, port=5432, dbname=’my_db’, user=’Super User’, password=’cheese’)

Fields can be omitted and they will not be sent, or default will be used. For example, if your ident specifies a default user to be your system user, or if you don’t have a password for localhost accounts, etc. , then don’t set those fields.

Individual Connections

While the global provides the defaults to use, you may also create standalone connections (for example, to copy data from one database and then connect and save to another).

You will also need to create and pass along a connection object when doing transactions.

The getDatabaseConnection method will return a new connection. If you don’t provide any arguments, it will inherit the connection info from the global connection. Any arguments you do provide will override the associated global connection parameter for the returned connection.

# Get a connection same settings as global connection

dbConn = getDatabaseConnection()

# Get a connection same settings as global connection (for transactions)

dbConn = getDatabaseConnection(isTransactionMode=True)

# Get a connection using same settings but connect to a different database:

dbConnBak = getDatabaseConnection(db_name=’bak_my_db’)

Models

This section will deal with your ORM models and the associated methods. Models are also used with the query builder, which is covered in the “Query Builder” section.

Your SQL tables should be represented by a DatabaseModel object ( ichorORM.DatabaseModel ).

Each table is expected to have a serial sequence primary key (generally called “id”) for sanity and performance reasons.

You may find it useful to add relevant methods to this model object.

from ichorORM import DatabaseModel

class Person(DatabaseModel):

# TABLE_NAME - This is the name of the corrosponding table in your database

TABLE_NAME = ‘Person’

# FIELDS - A list of all fields on this table

FIELDS = [ ‘id’, ‘first_name’, ‘last_name’, ‘age’, ‘birthday’, ‘gender’, ‘eye_color’, ‘ethnicity’, ‘title’ ]

# REQUIRED_FIELDS - A list of NOT NULL fields which will validate prior to

# insertObject/createAndSave (cannot be None or ValueError raised)

REQUIRED_FIELDS = [ ‘first_name’ ]

# DEFAULT_FIELD_VALUES - A map for client-side defaults.

# When a new object is created, the fields are assigned these values

# if not explicitly set to something else

DEFAULT_FIELD_VALUES = { ‘title’ : ‘General Employee’ }

# PRIMARY_KEY - If your primary serial key is not ‘id’, name it here

# PRIMARY_KEY = ‘serial_num’

Creating and Saving an entry

All field names found in the ‘FIELDS’ array on your model can be set by passing as a kwarg to __init__.

They also become variable members of the object.

Any defaults found in DEFAULT_FIELD_VALUES will be applied here if a different value isn’t explicitly set.

personObj = Person(first_name=’Tim’, age=30, gender=’male’, eye_color=’Hazel’)

print ( “%s is a %d year old %s whose job title is %s.” %( personObj.first_name, personObj.age, personObj.gender, personObj.title ) )

The above code will output “Tim is a 30 year old male whose job title is General Employee.”

To save this object, we call the insertObject method

personObj.insertObj()

This will perform an INSERT of that person, and it will set the primary key on the personObj.

So if the next serial sequence item was 5, personObj.id would now == 5.

This commits the transaction right away. How to group multiple actions within a single transaction will be covered later.

.

You may also use the static method createAndSave to immediately save and return a given object:

personObj = Person.createAndSave(first_name=’Tim’, age=30, gender=’male’, eye_color=’Hazel’)

This will have all the same field values, including primary key set, as the earlier insert method.

createAndSave also supports transactions which will be covered later.

Updating an entry

Any model that is saved can be updated simply by setting the appropriate field values and calling updateObject as seen below:

personObj.last_name = ‘Johnson’

personObj.title = ‘General Manager’

# updateObject method - Provide a list of fields to update

personObj.updateObject( [‘last_name’, ‘title’] )

This method also supports transactions, with the default being immediate commit.

Deleting an entry

An object can be deleted by calling the delete method

oldId = personObj.delete()

This will return the old primary key (in oldId above) and clear the primary key field off “personObj.”

Fetching an entry

An entry can be fetched via several means. More advanced means are covered in latter sections, this will focus on the methods available through DatabaseModel

By primary key, use get:

personObj = Person.get(5) # If primary key is 5

By field values, use filter:

personObj = Person.filter(age__gt=20, gender=’male’, eye_color__in=[‘Brown’, ‘Hazel’])

This will return a list of all Person objects where age > 20 and gender = ‘male’ and eye color is one of “Brown” or “Hazel”.

The standard “filter” rules apply here, double underscore and operation.

* = or __eq= - Equals operator

* __ne= - Not Equal ( <> ) operator

* __ is or __isnot - IS or IS NOT ( you can use *None* to represent NULL, or the SQL\_NULL constant )

* __in or __notin - IN or NOT IN a list of values

* __isnull=True or __isnull=False - Compare IS NULL or IS NOT NULL.

Or to fetch all objects of a given table, use the all method

allPeople = Person.all()

Any objects fetched can be updated just by changing property values and calling .updateObject

Other Methods

asDict - This will return a dict of the field names -> values

personDict = personObj.asDict()

Foreign Relations

Foreign relations ( a foreign key that points to another object(s) ) can be defined easily by implementing the classmethod DatabaseModel.getModelRelations

For example, consider that you have a model Person with primary key “id”, and a model Meal that contains a foreign key reference “id_person”. You can implement these relations like so:

Add “meals” relation to Person to fetch all Meals where Meal.id_person = Person.id

from ichorORM.relations import OneToManyRelation

class Person(DatabaseModel):

@classmethod

def getModelRelations(cls):

# Import the model here to prevent circular reference

from .Meal import Meal

# Reference Person.id to Meal.id_person

mealRelation = OneToManyRelation(‘id’, Meal, ‘id_person’)

return {

‘meals’ : mealRelation, # Add property “Person.meals” which will follow this relation

Meal : mealRelation, # Add the same relation available by calling Person.getRelation(Meal)

}

Add “person” relation to Meal to fetch the Person where Meal.id_person = Person.id

from ichorORM.relations import OneToOneRelation

class Meal(DatabaseModel):

@classmethod

def getModelRelations(cls):

# Import the model here to prevent circular reference

from .Person import Person

# Reference Meal.id_person to Person.id

personRelation = OneToOneRelation(‘id_person’, Person, ‘id’)

return {

‘person’ : personRelation, # Add property “Meal.person” which will follow this relation

Person : personRelation, # Add the same relation available by calling Meal.getRelation(Person)

}

There are two ways to use this relation:

By property

For any item in the dict returned by getModelRelations where the key is a string, a property is added to the model which, upon access, will follow the relation.

For instance, in the above examples, if I have an instance of a Meal object, I can access the related person like so:

myMealObj = …. # Fetch the Meal object

personWhomAteMeal = myMealObj.person # follow the relation with key ‘person’ to return the Person where id = myMealObj.id_person

And from an instance of a Person object I can access a list of all related meals like so:

myPersonObj = …. # Fetch the Person object

myPersonsMeals = myPersonObj.meals # follow the relation with key “meals” to return all Meal objects where id_person = myPersonObj.id

Keep in mind that each time this property is accessed a query is executed to follow this relation. Thus, if you want to fetch the relation once then save the result to a local variable and use that local variable instead of re-accessing the property.

By method

For any item in the dict returned by getModelRelations you can pass the key to DatabaseModel.getRelated

For instance, using the above examples, if I have an instance of a Meal object I can access the related person like so:

myMealObj = ….. # Fetch the Meal object

# We can use the string ‘person’ as returned in getModelRelations

personWhomAteMeal = myMealObj.getRelated(‘person’)

# Or we can use the model itself which we also provided as a key returned by getModelRelations

personWhomAteMeal = myMealObj.getRelated(Person)

For now, these relations are “read-only”, that is, assinging myMealObj.person = someOtherPerson is not effective.

Transactions

ichorORM supports transactions easily to ensure atomic operations which affect several tables, and for bulk-actions.

Each transaction needs a connection

Start by obtaining a new connection you will use for this transaction. Make sure to set isTransactionMode to True to enable read-commit instead of auto-commit mode

dbConn = getDatabaseConnection(isTransactionMode=True)

For use on model methods

This section covers how to do transactions within the DatabaseModel methods. Doing a transaction with the query builder will be discussed later.

Each of the “save action” methods ( insertObject, updateObject, createAndSave ) take two parameters you will set to performa transaction.

These are “dbConn” in which you will pass the transaction connection you opened in step 1, and “doCommit” which you will set to False. When you are done, you can call commit on the connection object.

dbConn = getDatabaseConnection(isTransactionMode=True)

person1 = Person(first_name=’John’, last_name=’Smith’, age=34)

person2 = Person(first_name=’Jane’, last_smith=’Doe’, age=29)

person3 = Person(first_name=’Bob’, last_name=’Doll’, age=69)

person1.insertObject(dbConn=dbConn, doCommit=False)

person2.insertObject(dbConn=dbConn, doCommit=False)

person3.insertObject(dbConn=dbConn, doCommit=False)

dbConn.commit()

or

dbConn = getDatabaseConnection(isTransactionMode=True)

person1 = Person.createAndSave(first_name=’John’, last_name=’Smith’, age=34, dbConn=dbConn, doCommit=False)

person2 = Person.createAndSave(first_name=’Jane’, last_smith=’Doe’, age=29, dbConn=dbConn, doCommit=False)

person3 = Person.createAndSave(first_name=’Bob’, last_name=’Doll’, age=69, dbConn=dbConn, doCommit=False)

dbConn.commit()

For updates:

dbConn = getDatabaseConnection(isTransactionMode=True)

peopleChangingTitle = People.filter(title=’Customer Service Rep’)

for person in peopleChangingTitle:

person.title = ‘Customer Care Officer’

person.updateObject( [‘title’], dbConn=dbConn, doCommit=False)

dbConn.commit()

This will rename all people with the title “Customer Service Rep” to the new title “Customer Care Officer” in one atomic transaction.

Rollback

You can trigger a rollback by calling “rollback” on the connection method during a transaction

dbConn.rollback()

This is required to be called if the transaction fails (throws an exception) and you want to use this connection again (as this will signify the end of the transaction block)

For use in query builders

Each of the execute* methods ( execute, executeGetRows, executeGetObjs, executeInsert, executeUpdate, executeDelete, etc. ) has a “dbConn” parameter. Any non-read action also has a “doCommit.” These have the same meaning as before, so pass the connection to the operations and call “commit” when ready to execute.

The transaction mode is READ_COMMITTED when isTransactionMode=True, so any of the queries will return right away and any writes (update/insert) will execute when “commit” is called on the connection object.

Query Builder

Although the ORM and DatabaseModel are very simple and complete, for optimization or complex projects you may prefer to use the query builder.

Most query builder classes take one or more DatabaseModel’s as parameters. Depending on the methods called, you can use query builder and still get objects returned.

We will start with a basic select query:

Simple Select Query

The simplest query is the Select Query.

selQ = SelectQuery(Person, selectFields=[‘first_name’, ‘age’], orderByField=’age’, orderByDir=’DESC’, limitNum=50)

rows = selQ.executeGetRows()

This will return a list of tuples, each containing first_name followed by age. Each one of these tuples is a returned row. They will be sorted in descending order based on the ‘age’ field. No more than 50 items will be returned.

Default is to select all fields, no explicit order by, no explicit order direction, and no limit.

You can also have the Model objects returned with all selected fields filled in.

selQ = SelectQuery(Person, orderByField=’age’, orderByDir=’DESC’)

peopleObjs = selQ.executeGetObjs()

This will fetch all fields and return People objects for each one. This would be the same as calling Person.all(), except the results are ordered by age descending.

Wheres

Now it’s not very useful to return all objects, we want to be able to filter them.

All query types have a method, addStage which takes 1 argument, “AND” or “OR” (default “AND”). This creates a group in the WHERE clause based on conditions, added via addCondition. If “OR” is selected, each conditional in this group will be linked with an “OR”, otherwise “AND”.

addCondition takes a 1. Field name, 2. Field operation, 3. Right-side value

For example:

selQ = SelectQuery(Person)

selQWhere1 = selQ.addStage(‘AND’)

selQWhere1.addCondition(‘age’, ‘>’, 30)

selQWhere1.addCondition(‘eye_color’, ‘=’, ‘Blue’)

selQWhere2 = selQ.addStage(‘OR’)

selQWhere2.addCondition(‘age’, ‘<’, 35)

selQWhere2.addCondition(‘last_name’, ‘=’, ‘Smith’)

matchedPeople = selQ.executeGetObjs()

This will generate a query with two “groups” in the WHERE clause. The executed query will look something like this:

SELECT * FROM person WHERE ( age > 30 AND eye_color = ‘Blue’ ) AND ( age < 35 OR last_name = ‘Smith’ )

Notice the top-level stages are joined by an “AND”. You can get as complicated as you want here!

The object returned by addStage also has an addStage method to add sub stages.

So, for example, if I wanted to filter where (age is > 30 and eye color is ‘Blue’) OR ( age < 35 or last_name = ‘Smith’ ):

selQ = SelectQuery(Person)

selQOuterWhere = selQ.addStage(‘OR’)

selQWhere1 = selQOuterWhere.addStage(‘AND’)

selQWhere1.addCondition(‘age’, ‘>’, 30)

selQWhere1.addCondition(‘eye_color’, ‘=’, ‘Blue’)

selQWhere2 = selQOuterWhere.addStage(‘OR’)

selQWhere2.addCondition(‘age’, ‘<’, 35)

selQWhere2.addCondition(‘last_name’, ‘=’, ‘Smith’)

matchedPeople = selQ.executeGetObjs()

so basically creating an “outer stage” set to OR and adding substages to that, we now get a query like:

SELECT * FROM person WHERE ( ( age > 30 AND eye_color = ‘Blue’ ) OR ( age < 35 OR last_name = ‘Smith’ ) )

Advanced Select / Join Multiple Tables

SelectInnerJoinQuery

This performs an inner join between multiple tables. This should generally not be used over the more powerful SelectGenericJoinQuery

Pass as the first argument a list of Models to use.

For selectFields, prefix with the table name ( e.x. “person.age” )

For conditionals, do the same. Make sure conditionals perform the joins!

selQ = SelectInnerJoinQuery( [Person, Meal] )

selQWhere = selQ.addStage(‘AND’)

selQWhere.addCondition(‘meal.id_person’, ‘=’, ‘person.id’)

# As dict objs

dictObjs = selQ.executeGetDictObjs()

# Or as a mapping

mapping = selQ.executeGetMapping()

This will generate a query like

SELECT person.*, meal.* FOR person, meal WHERE meal.id_person = person.id

SelectGenericJoinQuery

This is the prefered method for getting the results of joined tables.

It takes the primary model ( the FROM ) as the first argument.

For selectFields, prefix with the table name ( e.x. “person.age” )

selQ = SelectGenericJoinQuery( Person, selectFields=[‘Person.first_name’, ‘Person.last_name’, ‘Meal.item_name’] )

selQWhere = selQ.addStage()

selQWhere.addCondition(‘age’, ‘>’, 18)

Join on another table by calling joinModel passing the model to join, a join type constant (from ichorORM.constants) JOIN_* (e.x. JOIN_INNER, JOIN_LEFT, JOIN_RIGHT, JOIN_OUTER_FULL) , and “AND” or “OR” outer-mode for this stage.

The stage is returned so you can call .addCondition on it to add conditionals on the join line. Don’t forget to join your tables with a condition here!

joinWhere = selQ.joinModel( Meal, ‘INNER’, ‘AND’ )

joinWhere.addCondition( ‘id_person’, ‘=’, Person.PRIMARY_KEY )

# As dict objs

dictObjs = selQ.executeGetDictObjs()

# Or as a mapping

mapping = selQ.executeGetMapping()

This will generate a more conventional joined-select query, like so:

SELECT Person.first_name, Person.last_name, Meal.item_name FROM Person

INNER JOIN Meal ON ( Meal.id_person = Person.id )

WHERE

person.age > 18

Results

If you call executeGetDictObjs you will get a list of DictObjs. This is an object where access is supported either via dot (.field) or sub ([‘field’]). The first level is the table name, the second level is the field names. For example, obj[‘person’][‘first_name’] would be the person.first_name field.

If you call executeGetMapping you will get a list of OrderedDict (in same order specified in selectFields). For example, obj[‘person.first_name’] if you named the field like that in selectFields, or if you just had selectFields=[‘first_name’… ] then it would be obj[‘first_name’]

Update Query

Update queries use the UpdateQuery object. The stages work the same as in a SelectQuery.

Use the method setFieldValue to update the value of a field.

upQ = UpdateQuery(Person)

upQ.setFieldValue(‘title’, ‘Customer Care Expert’)

upQWhere = upQ.addStage()

upQWhere.addCondition(‘title’, ‘=’, ‘Customer Service Rep’)

upQ.executeUpdate()

execute can also be used as an alias to executeUpdate

Also keep in mind that you can pass a getDatabaseConnection(isTransactionMode=True) to executeUpdate and set doCommit=False to link multiple updates or inserts and updates into a single transaction (executed when dbConn.commit() is called)

Insert Query

An InsertQuery object is used to build queries to perform inserts.

insQ = InsertQuery(Person)

insQ.setFieldValue(‘first_name’, ‘Tim’)

insQ.setFieldValue(‘age’, 22)

personId = insQ.executeInsert()

execute can also be used as an alias to executeInsert

The “returnPk” argument (default True) causes the primary key of the Person model to be returned. This is returned immediately, even when within a transaction (read-commit).

Also keep in mind that you can pass a getDatabaseConnection(isTransactionMode=True) to executeInsert and set doCommit=False to link multiple inserts or inserts and updates into a single transaction (executed when dbConn.commit() is called)

Delete Query

A DeleteQuery object is used to build queries to delete records

delQ = DeleteQuery(Person)

delQWhere = delQ.addStage()

delQWhere.addCondition(‘age’, ‘<’, 18)

delQWhere.executeDelete()

execute can also be used as an alias to executeDelete

Keep in mind you can also delect records in a transaction by passing dbConn and doCommit=False to execute or executeDelete. Changes will be applied when commit is called on that connection.

Transactions within Query Builder

To use transactions with query builder statements, get a isTransactionMode=True Database connection like before and pass it to the execute* methods along with doCommit=False. When ready, call commit on the connection object.

dbConn = getDatabaseConnection(isTransactionMode=True)

magicCake = Meal(food_group=’desert’, item_name=’cake’, price=‘5.99’)

# Everyone on their birthday will get a magic cake

for person in birthdayPeople:

magicCakeCopy = copy.deepcopy(magicCake)

magicCakeCopy.id_person = person.id

magicCakeCopy.insertObject(dbConn=dbConn, doCommit=False)

# Everyone who eats the magic cake has their eyes turn blue

upQ = UpdateQuery(Person)

upQ.setFieldValue(‘eye_color’, ‘Blue’)

upQ.execue(dbConn=dbConn, doCommit=False)

# Execute the transaction, but only commit on success. If fail, exception will be raised.

try:

dbConn.commit()

except Exception as e:

print ( ‘Unable to run birthday transaction, rolling back. Error is %s %s’ %(str(type(e)), str(e)))

Handling Errors

If a query fails, an exception will be raised (a psycopg2 exception).

For transactions, you can wrap the “dbConn.commit” call in a try/except loop.

For any immediate commit actions, the execute* * method or the *insertObject/updateObject/createAndSave method will raise an exception upon error.

Using explicit SQL / Special Values

NULL

There are a few ways to represent a value of “NULL.” The most common is that ichorORM associates NULL with None.

None will be used when fields have a NULL value, and can be used with filtering as a replacement for NULL.

You may also find it useful sometimes to use “ichorORM.constants.SQL_NULL”.

If you do a query like:

myObjs = MyModel.filter(some_field=None)

ichorORM will automatically convert the “equals” operator to the “is” operator; that is to say you would have a query like:

SELECT * FROM MyModel WHERE some_field IS NULL

which will return results as expected, versus:

SELECT * FROM MyModel WHERE some_field = NULL

which would return NOTHING (postgres is pedantic that you must use “is” and “is not” with NULL)

Explicit Query Strings

While the given ORM functions should cover 98% of use cases, sometimes you want to use a call to an explicit sql function or otherwise.

You can use the same functions such as “setFieldValue” but instead of interpreting the value as a string (thus quoting / escaping) you can provide explicit SQL by wrapping the value in a QueryStr type.

Example:

import datetime

from ichorORM.query import QueryStr, SelectQuery, UpdateQuery

today = datetime.date.today()

# Find all the “Person” objects

birthdayQ = SelectQuery(Person, selectFields=[‘id’])

# Filter on all folks who had birthday today.

# Note: we can directly pass a datetime.date/datetime.datetime object for TIMESTAMP fields

birthdayQWhere = birthdayQ.addStage()

birthdayQWhere.addCondition(‘birthday’, ‘>=’, today)

birthdayQWhere.addCondition(‘birthday’, ‘<’, today + datetime.timedelta(days=1))

# Execute the query and return rows

birthdayQRows = birthdayQ.executeGetRows()

# Rows are returned with columns matching #selectFields in SelectQuery.

# In this case, we are only selecting ‘id’ and thus take first col in every row

birthdayIds = [ row[0] for row in birthdayQRows ]

upQ = UpdateQuery(Person)

# Increment age + 1 for people whose birthday is today

# NOTE: WE USE QueryStr HERE FOR EXPLICIT “age + 1” rather than a string holding value ‘age + 1’

upQ.setFieldValue(‘age’, QueryStr(‘age + 1’))

# Qualify the WHERE to be the birthday ids

upQWhere = upQ.addStage()

upQWhere.addCondition(‘id’, ‘in’, birthdayIds)

try:

upQ.execute()

except Exception as e:

print ( “Failed to increment age of birthday people. Error is %s %s” %(str(type(e)), str(e)) )

This example would execute a select to gather ids, and then perform an update like this:

UPDATE Person SET age = age + 1 WHERE id in ( …list_of_ids… )

This is also a drawn-out example for documentation/tutorial purposes. It executes a SELECT query, returns the ids back to the client, which then issues an UPDATE query using those ids. This can all be simplified by just using the SELECT conditionals within the Update query itself:

upQ = UpdateQuery(Person)

upQ.setFieldValue(‘age’, QueryStr(‘age + 1’))

upQWhere = upQ.addStage()

upQWhere.addCondition(‘birthday’, ‘>=’, today)

upQWhere.addCondition(‘birthday’, ‘<’, today + datetime.timedelta(days=1))

try:

upQ.execute()

except Exception as e:

print ( “Failed to increment age of birthday people. Error is %s %s” %(str(type(e)), str(e)) )

Or the entire condition value can be a QueryStr:

upQWhere.addCondition(‘birthday’, ‘BETWEEN’, QueryStr(“”“date_trunc(‘day’, CURRENT_TIMESTAMP) AND (day_trunc(‘day’, CURRENT_TIMESTAMP) + INTERVAL ‘23:59:59’)))

Or a tuple of two items (range start, range end), either as “date-like” objects or QueryStr, or a mix thereof

upQWhere.addCondition(‘birthday’, ‘BETWEEN’, [ QueryStr(“”“date_trunc(‘day’, CURRENT_TIMESTAMP)”“”), today + datetime.timedelta(days=1)] )

Embedded Queries

You may embed subqueries directly using the QueryStr object, or you can embed a SelectQuery you have created.

# Create the UpdateQuery object on a Person

upQ = UpdateQuery(Person)

# Increment age + 1 for people whose ate birthday cake today

upQ.setFieldValue(‘age’, QueryStr(‘age + 1’))

# Create a subqery that will select the id_person from a Meal object with matching critera

mealIdSelQ = SelectQuery(Meal, selectFields=[‘id_person’])

mealIdSelQWhere = mealIdSelQ.addStage()

mealIdSelQWhere.addCondition(‘food_name’, ‘LIKE’, ‘%Cake’)

mealIdSelQWhere.addCondition(‘consumed_date’, datetime.date.today() )

# Create the WHERE query to embed

upQWhere = upQ.addStage()

# select id from the subquery

upQWhere.addCondition(‘id’, ‘in’, mealIdSelQ)

try:

upQ.execute()

except Exception as e:

print ( “Failed to increment age of birthday people. Error is %s %s” %(str(type(e)), str(e)) )

This will generate a query like:

UPDATE Person SET age = age + 1 WHERE id in (SELECT id_person FROM Meal WHERE food_name LIKE ‘%Cake’ AND consumed_date = ‘2018-07-04’::date )

Aggregate Functions

You may wish to select some aggregate data from one of your models, such as the average of some field or the sum of another.

To accomplish this, use a QueryStr containing the aggregate expression within selectFields.

For example,

# Build a SelectQuery with our aggregate functions specified within selectFields

selQ = SelectQuery(MyPersonModel, selectFields=[ QueryStr(‘AVG(age)’), QueryStr(‘MAX(age)’), QueryStr(‘MAX(birth_day)’), QueryStr(‘MIN(birth_month)’), QueryStr(‘MIN(age)’) ])

# We need to use executeGetRows here, not executeGetObjs, as the models do not have fields for the aggregates.

results = selQ.executeGetRows()

# Because every entry in #selectFields is an aggregate function,

# we will get one row back containing the results in the same

# order as #selectFields specified

(gotAvgAge, gotMaxAge, gotMaxBirthDay, gotMinBirthMonth, gotMinAge) = results[0]

Additional Libraries

You may find it useful to combine ichorORM with QueryableList ( https://github.com/kata198/QueryableList )

This will allow you to further refine query results client-side (after data has been received from the postgresql database) ORM-style.

For example:

import QueryableList

adultPeople = People.filter(age__gte=18)

adultPeople = QueryableList.QueryableListObjs(adultPeople)

adultTims = adultPeople.filter(first_name=’Tim’)

In this simple example, we query the database for any People that have an age >= 18. Then, client-side using QueryableList, we further refine the results to filter out only those whose first name is ‘Tim’

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