sqlbind 0.2

sqlbind allows to bind parameters in text based raw SQL queries

sqlbind

sqlbind allows to bind parameters in text based raw SQL queries.

>>> q = sqlbind.Dialect.default()
>>> email = '[e-mail]'
>>> sql = f'SELECT * FROM users WHERE email = {q/email}'
>>> sql
'SELECT * FROM users WHERE email = ?'
>>> q
['[e-mail]']
>>> data = conn.execute(sql, q)

Supports all DBAPI parameter styles. Isn't limited by DBAPI compatible drivers and could be used with anything accepting raw SQL query and parameters in some way. For example sqlbind could be used with SQLAlchemy textual queries. Or with clickhouse-driver's non-DBAPI interface.

Installation

pip install sqlbind

Motivation

ORMs are great and could be used effectively for a huge number of tasks. But after many years with SQLAlchemy I've noticed some repeating patterns:

• It's really not an easy task to decipher complex SQLAlchemy expression back into SQL. Especially when CTEs, sub-queries, nested queries or self-referential queries are involved. It composes quite well but it takes too much effort to write and read SQLAlchemy queries. For novices it could be a hard time to deal with it.

• Most of reporting queries are big enough already not to be bothered with ORMs and use raw SQL anyway. This kind of SQL often requires dynamic constructs and becomes string fiddling contraption.

• For a few tasks ORMs bring too much overhead and the only solution is to get down to raw DBAPI connection and raw SQL.

• (Minor personal grudge, please ignore it) For some ORMs (like Django ORM) your SQL intuition could be useless and requires deep ORM understanding. To the side: sqlalchemy hybrid properties, cough.

It boils down to one thing: from time to time you have to write raw SQL queries. I could highlight 3 types of queries:

1. Fixed queries. They don't contain any parameters. For example SELECT id, name FROM users ORDER BY registered DESC LIMIT 10. In general fixed queries or fixed query parts compose well and don't require any special treatment. Python's f-strings are enough.

2. Static queries. They contain parameters but structure is fully known beforehand. For example SELECT id, name FROM users WHERE email = :email LIMIT 1. They are also could be composed without large issues, especially for connection drivers supporting named parameters (:param, %(param)s) and accepting dicts as parameters. Although for positional connection drivers (%s, ?) composition requires careful parameter tracking and queries could be fragile to change.

3. Dynamic queries. Query part presence could depend on parameter value or external condition. For example to provide result on input filter you have to add CTE and corresponding JOIN to a query. Or add filters only for non None input values. ORMs are effective for composing such queries. Using raw SQL are almost impossible for abstraction and leads to a complex boilerplate heavy source code.

Note: here and in following sections I deliberately use simple examples. In real life there is no need to use sqlbind for such kind of queries.

Note: by composing I mean ability to assemble a final query from parts which could be abstracted and reused.

sqlbind tries to address issues with static and dynamic query types. It tracks parameter binds and could help with dynamic query parts.

Quick start

Some things to consider:

• sqlbind tries to provide an API for a simple composition of raw SQL. Most operations return string-like objects ready to be inserted in the final query. sqlbind does trivial things and is easy to reason about.

• There is a large set of functions/methods to address dynamic queries but you haven't use it inline in a single query string. You could use variables to keep query parts and stitch resulted SQL from these parts.

• This README misses large portions of API. Feel free to explore doc strings with examples of fully strictly type-hinted sqlbind's source code!

General use case looks like:

# a global alias to dialect used by connection backend
QParams = sqlbind.Dialect.some_dialect

def get_my_data(value1, value2):
    # Construct empty fresh sqlbind.QueryParams
    q = QParams()

    # Use `q` to bind parameter values in SQL string.
    sql = f'SELECT * FROM table WHERE field1 = {q/value1} AND field2 > {q/value2}'

    # Pass query and parameters into connection's execute.
    return get_connection().execute(sql, q).fetchall()

Static queries

For queries or query parts with a known structure the most simple way to bind a parameter is to use bind operator /:

>>> value = 10
>>> q = sqlbind.Dialect.default()
>>> q/value
'?'
>>> q
[10]

It returns a placeholder for a corresponding dialect and adds parameter's value to q object. That's basically all.

>>> date = "2023-01-01"
>>> q = sqlbind.Dialect.default_named()
>>> f'SELECT * FROM users WHERE registered > {q/date}'
'SELECT * FROM users WHERE registered > :p0'
>>> q
{'p0': '2023-01-01'}

Note: there is no much value in sqlbind if you have only static queries and use connection backends accepting named parameters.

Dynamic queries

Here begins a fun part. We can't use simple binds for dynamic queries. For example we have a function returning recently registered users:

def get_fresh_users(registered_from: datetime):
    q = QParams()  # an alias to some dialect to construct sqlbind.QueryParams instance
    sql = f'''\
        SELECT * FROM users
        WHERE registered > {q/registered_from}
        ORDER BY registered
    '''
    return conn.execute(sql, q)

And later there is a new requirement for the function. It should return only enabled or only disabled users if corresponding argument is passed.

def get_fresh_users(registered_from: datetime, enabled: Optional[bool] = None):
    q = QParams()

    if enabled is not None:
        enabled_filter = f' AND enabled = {q/enabled}'
    else:
        enabled_filter = ''

    sql = f'''\
        SELECT * FROM users
        WHERE registered > {q/registered_from} {enabled_filter}
        ORDER BY registered
    '''
    return conn.execute(sql, q)

It looks almost pretty. See how q/enabled helped to track additional parameter. But you can predict where we are going. Another one or two additional filters and it would be a complete mess. Take note how WHERE lost AND between two filters.

q-templates

In reality bind operator / is a sugar on top of generic sqlbind's API to bind parameters via q-templates.

>>> q = sqlbind.Dialect.default()
>>> q('field BETWEEN {} AND {}', 10, 20)
'field BETWEEN ? AND ?'
>>> q
[10, 20]

QueryParams q object is also a callable accepting a template with {} placeholders and following parameters to substitute. q/value is same as calling q('{}', value)

>>> q/10
'?'
>>> q('{}', 10)
'?'

You could use q-templates to bind parameters in complex SQL expressions.

Conditionals

q.cond, q.not_none and q.not_empty could render a q-template as an empty string based on input parameters.

>>> enabled = True
>>> q.cond(enabled is not None, ' AND enabled = {}', enabled)
' AND enabled = ?'
>>> enabled = None
>>> q.cond(enabled is not None, ' AND enabled = {}', enabled)
''

q.cond is a generic form. To remove a repetition (enabled is not None/enabled) when value is used both in a condition and as a parameter value there are two helpers for most common cases:

• q.not_note: to check value is not None.
• q.not_empty: to check value's trueness (bool(value) is True).

>>> enabled = True
>>> q.not_none(' AND enabled = {}', enabled)
' AND enabled = ?'
>>> enabled = None
>>> q.not_none(' AND enabled = {}', enabled)
''

Let's try it in the function:

def get_fresh_users(registered_from: datetime, enabled: Optional[bool] = None):
    q = QParams()

    enabled_filter = q.not_none(' AND enabled = {}', enabled)

    sql = f'''\
        SELECT * FROM users
        WHERE registered > {q/registered_from} {enabled_filter}
        ORDER BY registered
    '''
    return conn.execute(sql, q)

Hmm. But really nothing was changed. You could write previous code with ternary if/else and it would look the same from semantic standpoint. May be use it inline?

def get_fresh_users(registered_from: datetime, enabled: Optional[bool] = None):
    q = QParams()

    sql = f'''\
        SELECT * FROM users
        WHERE registered > {q/registered_from}
              {q.not_none(' AND enabled = {}', enabled)}
        ORDER BY registered
    '''
    return conn.execute(sql, q)

Ugh. Abomination, to say at least.

• AND in the middle of a cryptic expression.
• q.not_none and enabled is far away and it's not obvious they are connected
• expression is too long and noisy

Let's tackle issues bit by bit.

AND_/OR_ prependers

Prependers could render not empty inputs with corresponding prefixes and empty string otherwise.

>>> AND_('field1 > 1', 'field2 < 1')
'AND field1 > 1 AND field2 < 1'
>>> OR_('field1 > 1', 'field2 < 1')
'OR field1 > 1 OR field2 < 1'
>>> AND_(q.not_none('enabled = {}', True))
'AND enabled = ?'
>>> AND_(q.not_none('enabled = {}', None))
''

Our function with prependers:

from sqlbind import AND_

def get_fresh_users(registered_from: datetime, enabled: Optional[bool] = None):
    q = QParams()

    sql = f'''\
        SELECT * FROM users
        WHERE registered > {q/registered_from}
              {AND_(q.not_none('enabled = {}', enabled))}
        ORDER BY registered
    '''
    return conn.execute(sql, q)

At least AND is almost on it's place in SQL structure.

Conditional markers

Conditional markers not_none/not_empty/cond allows to tie conditional property with variable itself.

>>> not_none/10
10
>>> not_none/None is sqlbind.UNDEFINED  # returns special UNDEFINED object
True
>>> q('enabled = {}', not_none/10)
'enabled = ?'
>>> q('enabled = {}', not_none/None)  # UNDEFINED parameters force expression to be rendered as empty
''

sqlbind.not_empty is the same as sqlbind.not_none but checks for value trueness. sqlbind.cond is almost always awkward to use inline in real life and exists largely for symmetry.

Rewritten function:

from sqlbind import AND_, not_none

def get_fresh_users(registered_from: datetime, enabled: Optional[bool] = None):
    q = QParams()

    sql = f'''\
        SELECT * FROM users
        WHERE registered > {q/registered_from}
              {AND_(q('enabled = {}', not_none/enabled))}
        ORDER BY registered
    '''
    return conn.execute(sql, q)

Almost there.

q-expressions

Any unknown attribute access to q object returns QExpr which has str conversion as an attribute name:

>>> str(q.field)
'field'
>>> str(q.table.field)
'table.field'
>>> str(q._.cond)  # to resolve conflicting names, you could use `q._.`(stare operator)
'cond'
>>> str(q._('"weird table"."weird column"'))  # or `q._`(pirate operator) to use any string
'"weird table"."weird column"'

q-expressions know about parent q object and define a number of infix operators allowing to bind a right parameter.

>>> q.field > 10
'field > ?'
>>> q.table.field == 20
'table.field = ?'
>>> q._.table.field == None
'table.field IS NULL'
>>> q._('"my column"') != None
'"my column" IS NOT NULL'
>>> q.field <= not_none/None  # conditional marks also work!
''
>>> q.field.IN(not_none/[10]) # BTW sqlbind has workaround for SQLite to deal with arrays in IN
'field IN ?'

It could look like a hack and fill ORMish but there is no any expression trees and tree compilation passes. q-expressions are immediately rendered as strings and simple to reason about.

Let's use q-expressions with the function:

from sqlbind import AND_, not_none

def get_fresh_users(registered_from: datetime, enabled: Optional[bool] = None):
    q = QParams()

    sql = f'''\
        SELECT * FROM users
        WHERE registered > {q/registered_from}
              {AND_(q.enabled == not_none/enabled)}
        ORDER BY registered
    '''
    return conn.execute(sql, q)

I have no any other tricks. It's the final inline version. I can't make it more pretty and readable.

WHERE prepender

But we could extract filters outside of f-strings and use sqlbind.WHERE prepender. It could help with readability of long complex filters.

from sqlbind import not_none, WHERE

def get_fresh_users(registered_from: datetime, enabled: Optional[bool] = None):
    q = QParams()

    filters = [
        q.registered > registered_from,
        q.enabled == not_none/enabled,
    ]

    sql = f'SELECT * FROM users {WHERE(*filters)} ORDER BY registered'
    return conn.execute(sql, q)

Or you could use & operator to join filters without list:

>>> filters = (q.registered > '2023-01-01') & (q.enabled == not_none/True)
>>> WHERE(filters)
'WHERE (registered > ? AND enabled = ?)'

— "Wait a minute. You said there is no expression trees and compilation! And all operations return strings!"

Expressions

I lied. Almost all methods and functions return sqlbind.Expr. It's a very shallow descendant of str with only __or__, __and__ and __invert__ reimplemented.

>>> q('enabled') & q('registered')
'(enabled AND registered)'
>>> type(q('enabled'))
<class 'sqlbind.Expr'>
>>> type(q.enabled == True)
<class 'sqlbind.Expr'>

All Expr instances could be composed with &, | and ~ (negate) operations. Sadly due to python's' precedence rules you have to wrap expressions into additional parens to make it work.

Conclusion

I kept promise you always deal with strings!