Package dev.morphia.aggregation.expressions

Class AccumulatorExpressions

java.lang.Object

dev.morphia.aggregation.expressions.AccumulatorExpressions

public final class AccumulatorExpressions
extends Object

Defines helper methods for accumulator expressions

Since:

2.0

Method Summary

Modifier and Type	Method	Description
static AccumulatorExpression	accumulator(String initFunction, String accumulateFunction, List<Expression> accumulateArgs, String mergeFunction)	Returns an array of unique expression values for each group.
static Expression	addToSet(Expression value)	Returns an array of unique expression values for each group.
static Expression	avg(Expression value, Expression... additional)	Returns an average of numerical values.
static Expression	bottom(Expression output, Sort... sortBy)	Returns the bottom element within a group according to the specified sort order.
static Expression	bottomN(Expression n, Expression output, Sort... sortBy)	Returns an aggregation of the bottom n elements within a group, according to the specified sort order.
static Expression	first(Expression value)	Returns a value from the first document for each group.
static Expression	firstN(Expression n, Expression input)	Returns an aggregation of the first n elements within a group.
static Expression	function(String body, Expression... args)	Defines a custom aggregation function or expression in JavaScript.
static Expression	last(Expression value)	Returns a value from the last document for each group.
static Expression	lastN(Expression n, Expression input)	Returns an aggregation of the last n elements within a group.
static Expression	max(Expression value)	Returns the highest expression value for each group.
static Expression	maxN(Expression n, Expression input)	Returns an aggregation of the max n elements within a group.
static Expression	min(Expression value)	Returns the lowest expression value for each group.
static Expression	minN(Expression n, Expression input)	Returns an aggregation of the min n elements within a group.
static Push	push()	Returns an array of all values that result from applying an expression to each document in a group of documents that share the same group by key.
static Expression	push(Expression value)	Returns an array of expression values for each group.
static Expression	stdDevPop(Expression value, Expression... additional)	Deprecated. use WindowExpressions.stdDevPop(Expression, Expression...)
static Expression	stdDevSamp(Expression value, Expression... additional)	Deprecated. use WindowExpressions.stdDevSamp(Expression, Expression...)
static Expression	sum(Expression first, Expression... additional)	Calculates and returns the sum of numeric values.
static Expression	top(Expression output, Sort... sortBy)	Returns the top element within a group according to the specified sort order.
static Expression	topN(Expression n, Expression output, Sort... sortBy)	Returns an aggregation of the top n elements within a group, according to the specified sort order.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

accumulator

public static AccumulatorExpression accumulator(String initFunction,
                                                String accumulateFunction,
                                                List<Expression> accumulateArgs,
                                                String mergeFunction)

Returns an array of unique expression values for each group. Order of the array elements is undefined.

Parameters:

initFunction - used to initialize the state. The init function receives its arguments from the initArgs expression.

accumulateFunction - used to accumulate documents. The accumulate function receives its arguments from the current state and accumulateArgs array expression.

accumulateArgs - Arguments passed to the accumulate function.

mergeFunction - used to merge two internal states.

Returns:

the new expression

Since:

2.1

MongoDB documentation

Aggregration Expression: $accumulator

addToSet

public static Expression addToSet(Expression value)

Returns an array of unique expression values for each group. Order of the array elements is undefined.

Parameters:

value - the value

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $addToSet

avg

public static Expression avg(Expression value,
                             Expression... additional)

Returns an average of numerical values. Ignores non-numeric values.

Parameters:

value - the value

additional - any subsequent expressions to include in the expression

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $avg

bottom

public static Expression bottom(Expression output,
                                Sort... sortBy)

Returns the bottom element within a group according to the specified sort order.

Parameters:

output - the expression listing the fields to use

sortBy - the sort order

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $bottom

bottomN

public static Expression bottomN(Expression n,
                                 Expression output,
                                 Sort... sortBy)

Returns an aggregation of the bottom n elements within a group, according to the specified sort order. If the group contains fewer than n elements, $bottomN returns all elements in the group.

Parameters:

n - the number of results per group and has to be a positive integral expression that is either a constant or depends on the _id value for $group

output - the expression listing the fields to use

sortBy - the sort order

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $bottomN

first

public static Expression first(Expression value)

Returns a value from the first document for each group. Order is only defined if the documents are in a defined order.

Parameters:

value - the value

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $first

firstN

public static Expression firstN(Expression n,
                                Expression input)

Returns an aggregation of the first n elements within a group. The elements returned are meaningful only if in a specified sort order. If the group contains fewer than n elements, $firstN returns all elements in the group.

Parameters:

n - the number of results per group and has to be a positive integral expression that is either a constant or depends on the _id value for $group

input - the expression listing the fields to use

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $firstN

function

public static Expression function(String body,
                                  Expression... args)

Defines a custom aggregation function or expression in JavaScript.

Parameters:

body - the function body

args - the function arguments

Returns:

the new expression

Since:

2.1

MongoDB documentation

Aggregration Expression: $function

last

public static Expression last(Expression value)

Returns a value from the last document for each group. Order is only defined if the documents are in a defined order.

Parameters:

value - the value

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $last

lastN

public static Expression lastN(Expression n,
                               Expression input)

Returns an aggregation of the last n elements within a group. The elements returned are meaningful only if in a specified sort order. If the group contains fewer than n elements, $lastN returns all elements in the group.

Parameters:

n - the number of results per group and has to be a positive integral expression that is either a constant or depends on the _id value for $group

input - the expression listing the fields to use

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $lastN

max

public static Expression max(Expression value)

Returns the highest expression value for each group.

Parameters:

value - the value

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $max

maxN

public static Expression maxN(Expression n,
                              Expression input)

Returns an aggregation of the max n elements within a group. The elements returned are meaningful only if in a specified sort order. If the group contains fewer than n elements, $maxN returns all elements in the group.

Parameters:

n - the number of results per group and n has to be a positive integral expression that is either a constant or depends on the _id value for $group.

input - the expression that is the input to $maxN. It is evaluated for each element in the group and $maxN preserves the maximum n values.

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $maxN

min

public static Expression min(Expression value)

Returns the lowest expression value for each group.

Parameters:

value - the value

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $min

minN

public static Expression minN(Expression n,
                              Expression input)

Returns an aggregation of the min n elements within a group. The elements returned are meaningful only if in a specified sort order. If the group contains fewer than n elements, $minN returns all elements in the group.

Parameters:

n - the number of results per group and n has to be a positive integral expression that is either a constant or depends on the _id value for $group.

input - the expression that is the input to $minN. It is evaluated for each element in the group and $minN preserves the minimum n values.

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $minN

push

public static Expression push(Expression value)

Returns an array of expression values for each group.

Parameters:

value - the value

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $push

push

public static Push push()

Returns an array of all values that result from applying an expression to each document in a group of documents that share the same group by key.

$push is only available in the $group stage.

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $push

sum

public static Expression sum(Expression first,
                             Expression... additional)

Calculates and returns the sum of numeric values. $sum ignores non-numeric values.

Parameters:

first - the first expression to sum

additional - any subsequent expressions to include in the sum

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $sum

top

public static Expression top(Expression output,
                             Sort... sortBy)

Returns the top element within a group according to the specified sort order.

Parameters:

output - the expression listing the fields to use

sortBy - the sort order

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $top

topN

public static Expression topN(Expression n,
                              Expression output,
                              Sort... sortBy)

Returns an aggregation of the top n elements within a group, according to the specified sort order. If the group contains fewer than n elements, $topN returns all elements in the group.

Parameters:

n - the number of results per group and has to be a positive integral expression that is either a constant or depends on the _id value for $group

output - the expression listing the fields to use

sortBy - the sort order

Returns:

the expression

Since:

2.3

Since server release

5.2

MongoDB documentation

Aggregration Expression: $topN

stdDevPop

@Deprecated
public static Expression stdDevPop(Expression value,
                                   Expression... additional)

Deprecated.

use WindowExpressions.stdDevPop(Expression, Expression...)

Returns the population standard deviation of the input values.

Parameters:

value - the value

additional - any subsequent expressions to include in the expression

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $stdDevPop

stdDevSamp

@Deprecated
public static Expression stdDevSamp(Expression value,
                                    Expression... additional)

Deprecated.

use WindowExpressions.stdDevSamp(Expression, Expression...)

Returns the sample standard deviation of the input values.

Parameters:

value - the value

additional - any subsequent expressions to include in the expression

Returns:

the new expression

MongoDB documentation

Aggregration Expression: $stdDevSamp