Documentation
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Overview ¶
Package filter parses and evaluates Chain filter expressions. A predicate is a boolean expression with zero or more placeholder values ($1, $2, etc) that are initially unconstrained. The predicate is evaluated in an environment (such as a transaction object or a UTXO) that determines the value of all non-placeholder terms. The predicate and its fixed values together constrain the placeholders. Function Eval finds the set of all placeholder values that satisfy the predicate.
Expressions in a filter expression have the following forms:
Form Type Subexpression types
expr1 "OR" expr2 bool bool, bool
expr1 "AND" expr2 bool bool, bool
ident "(" expr ")" bool list, bool
expr1 "=" expr2 bool any (must match)
expr "." ident any object
"(" expr ")" any any
ident any n/a
placeholder scalar n/a
string string n/a
int int n/a
ident is an alphanumeric identifier
placeholder is a decimal int with prefix "$"
scalar means int or string
string is single-quoted, and cannot contain backslash
int is decimal or hexadecimal (with prefix "0x")
list is a slice of environments
The environment is a map from names to values. Identifier expressions get their values from the environment map.
The form 'ident(expr)' is an existential quantifier. The environment value for 'ident' must be a list of subenvironments. The subexpression 'expr' is evaluated in each subenvironment, and if there exists one subenvironment for which 'expr' is true, the expression as a whole is true.
Filters are statically type-checked: if a subexpression doesn't have the appropriate type, Parse will return an error.
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ErrBadFilter = errors.New("invalid query filter")
ErrBadFilter is returned from Parse when it encounters an invalid filter expression.
Functions ¶
func FieldAsSQL ¶
FieldAsSQL returns a jsonb indexing SQL representation of the field.
Types ¶
type Field ¶
type Field struct {
// contains filtered or unexported fields
}
Field is a type for simple expressions that simply access an attribute of the queried object. They're used for GROUP BYs.
func ParseField ¶
ParseField parses a field expression (either an attrExpr or a selectorExpr).
type Predicate ¶
type Predicate struct {
Parameters int
// contains filtered or unexported fields
}
Predicate represents a parsed filter predicate.
func Parse ¶
Parse parses a predicate and returns an internal representation of the predicate or an error if it fails to parse.
func (Predicate) MarshalText ¶
MarshalText implements the encoding.TextMarshaler interface and returns a cleaned, canonical representation of the predicate.
Source Files