Predicate¶

class Predicate[source]¶

Bases: object

Represents a map entry predicate. Implementations of this class are basic building blocks for performing queries on map entries.

Special Attributes

The predicates that accept an attribute name support two special attributes:

__key - instructs the predicate to act on the key associated with an item.
this - instructs the predicate to act on the value associated with an item.

Attribute Paths

Dot notation may be used for attribute name to instruct the predicate to act on the attribute located at deeper level of an item. Given "full_name.first_name" path the predicate will act on first_name attribute of the value fetched by full_name attribute from the item itself. If any of the attributes along the path can’t be resolved, IllegalArgumentError will be thrown. Reading of any attribute from None will produce None value.

Square brackets notation may be used to instruct the predicate to act on the list element at the specified index. Given "names[0]" path the predicate will act on the first item of the list fetched by names attribute from the item. The index must be non-negative, otherwise IllegalArgumentError will be thrown. Reading from the index pointing beyond the end of the list will produce None value.

Special any keyword may be used to act on every list element. Given "names[any].full_name.first_name" path the predicate will act on first_name attribute of the value fetched by full_name attribute from every list element stored in the item itself under names attribute.

Handling of None

The predicates that accept None as a value to compare with or a pattern to match against if and only if that is explicitly stated in the method documentation. In this case, the usual equality logic applies: if None is provided, the predicate passes an item if and only if the value stored under the item attribute in question is also None.

Special care must be taken while comparing with None values stored inside items being filtered through the predicates created by the following methods: greater(), greater_or_equal(), less(), less_or_equal(), between(). They always evaluate to False and therefore never pass such items.

Implicit Type Conversion

If the type of the stored value doesn’t match the type of the value provided to the predicate, implicit type conversion is performed before predicate evaluation. The provided value is converted to match the type of the stored attribute value. If no conversion matching the type exists, IllegalArgumentError is thrown.

class PagingPredicate[source]¶

Bases: Predicate

This class is a special Predicate which helps to get a page-by-page result of a query.

It can be constructed with a page-size, an inner predicate for filtering, and a comparator for sorting. This class is not thread-safe and stateless. To be able to reuse for another query, one should call reset().

reset() → None[source]¶: Resets the predicate for reuse.

next_page() → int[source]¶

Sets page index to next page.

If new index is out of range, the query results that this paging predicate will retrieve will be an empty list.

Returns:: Updated page index

previous_page() → int[source]¶

Sets page index to previous page.

If current page index is 0, this method does nothing.

Returns:: Updated page index.

property page: int¶

The current page index.

Getter:: Returns the current page index.
Setter:: Sets the current page index. If the page is out of range, the query results that this paging predicate will retrieve will be an empty list. New page index must be greater than or equal to 0.

property page_size: int¶

The page size.

Getter:: Returns the page size.

sql(expression: str) → Predicate[source]¶

Creates a predicate that will pass items that match the given SQL where expression.

The following operators are supported: =, <, >, <=, >= ==, !=, <>, BETWEEN, IN, LIKE, ILIKE, REGEX AND, OR, NOT.

The operators are case-insensitive, but attribute names are case sensitive.

Example: active AND (age > 20 OR salary < 60000)

Differences to standard SQL:

We don’t use ternary boolean logic. field=10 evaluates to false, if field is null, in standard SQL it evaluates to UNKNOWN.
IS [NOT] NULL is not supported, use =NULL or <>NULL.
IS [NOT] DISTINCT FROM is not supported, but = and <> behave like it.

Parameters:: expression – The where expression.
Returns:: The created sql predicate instance.

equal(attribute: str, value: Any) → Predicate[source]¶

Creates a predicate that will pass items if the given value and the value stored under the given item attribute are equal.

Parameters:

attribute – The attribute to fetch the value for comparison from.
value – The value to compare the attribute value against. Can be None.

Returns:

The created equal predicate instance.

not_equal(attribute: str, value: Any) → Predicate[source]¶

Creates a predicate that will pass items if the given value and the value stored under the given item attribute are not equal.

Parameters:

attribute – The attribute to fetch the value for comparison from.
value – The value to compare the attribute value against. Can be None.

Returns:

The created not equal predicate instance.

like(attribute: str, pattern: str | None) → Predicate[source]¶

Creates a predicate that will pass items if the given pattern matches the value stored under the given item attribute.

Parameters:

attribute – The attribute to fetch the value for matching from.
pattern – The pattern to match the attribute value against. The % (percentage sign) is a placeholder for multiple characters, the _ (underscore) is a placeholder for a single character. If you need to match the percentage sign or the underscore character itself, escape it with the backslash, for example "\%" string will match the percentage sign. Can be None.

Returns:

The created like predicate instance.

Predicate¶

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