lucene/solr/solr-ref-guide/src/variables.adoc

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= Variables
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// to you under the Apache License, Version 2.0 (the
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// with the License. You may obtain a copy of the License at
//
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//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
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== The Let Expression
The `let` expression sets variables and returns
the value of the last variable by default. The output of any streaming expression or math expression can be set to a variable.
Below is a simple example setting three variables *`a`*, *`b`*
and *`c`*. Variables *`a`* and *`b`* are set to arrays. The variable *`c`* is set
to the output of the `ebeAdd` function which performs element-by-element
addition of the two arrays.
[source,text]
----
let(a=array(1, 2, 3),
b=array(10, 20, 30),
c=ebeAdd(a, b))
----
In the response, notice that the last variable, *`c`*, is returned:
[source,json]
----
{
"result-set": {
"docs": [
{
"c": [
11,
22,
33
]
},
{
"EOF": true,
"RESPONSE_TIME": 4
}
]
}
}
----
== Echoing Variables
All variables can be output by setting the `echo` variable to `true`.
[source,text]
----
let(echo=true,
a=array(1, 2, 3),
b=array(10, 20, 30),
c=ebeAdd(a, b))
----
When this expression is sent to the `/stream` handler it
responds with:
[source,json]
----
{
"result-set": {
"docs": [
{
"a": [
1,
2,
3
],
"b": [
10,
20,
30
],
"c": [
11,
22,
33
]
},
{
"EOF": true,
"RESPONSE_TIME": 0
}
]
}
}
----
A specific set of variables can be echoed by providing a comma delimited list of variables to the echo parameter.
Because variables have been provided, the `true` value is assumed.
[source,text]
----
let(echo="a,b",
a=array(1, 2, 3),
b=array(10, 20, 30),
c=ebeAdd(a, b))
----
When this expression is sent to the `/stream` handler it responds with:
[source,json]
----
{
"result-set": {
"docs": [
{
"a": [
1,
2,
3
],
"b": [
10,
20,
30
]
},
{
"EOF": true,
"RESPONSE_TIME": 0
}
]
}
}
----
== Caching Variables
Variables can be cached in-memory on the Solr node where the math expression
was run. A cached variable can then be used in future expressions. Any object
that can be set to a variable, including data structures and mathematical models, can
be cached in-memory for future use.
The `putCache` function adds a variable to the cache.
In the example below an array is cached in the `workspace` "workspace1"
and bound to the `key` "key1". The workspace allows different users to cache
objects in their own workspace. The `putCache` function returns
the variable that was added to the cache.
[source,text]
----
let(a=array(1, 2, 3),
b=array(10, 20, 30),
c=ebeAdd(a, b),
d=putCache(workspace1, key1, c))
----
When this expression is sent to the `/stream` handler it responds with:
[source,json]
----
{
"result-set": {
"docs": [
{
"d": [
11,
22,
33
]
},
{
"EOF": true,
"RESPONSE_TIME": 11
}
]
}
}
----
The `getCache` function retrieves an object from the cache by its workspace and key.
In the example below the `getCache` function retrieves the array the was cached above and assigns it to variable *`a`*.
[source,text]
----
let(a=getCache(workspace1, key1))
----
When this expression is sent to the `/stream` handler it responds with:
[source,json]
----
{
"result-set": {
"docs": [
{
"a": [
11,
22,
33
]
},
{
"EOF": true,
"RESPONSE_TIME": 11
}
]
}
}
----
The `listCache` function can be used to list the workspaces or the keys in a specific workspace.
In the example below `listCache` returns all the workspaces in the cache as an array of strings.
[source,text]
----
let(a=listCache())
----
When this expression is sent to the `/stream` handler it
responds with:
[source,json]
----
{
"result-set": {
"docs": [
{
"a": [
"workspace1"
]
},
{
"EOF": true,
"RESPONSE_TIME": 0
}
]
}
}
----
In the example below all the keys in a specific workspace are listed:
[source,text]
----
let(a=listCache(workspace1))
----
When this expression is sent to the `/stream` handler it responds with:
[source,json]
----
{
"result-set": {
"docs": [
{
"a": [
"key1"
]
},
{
"EOF": true,
"RESPONSE_TIME": 0
}
]
}
}
----
The `removeCache` function can be used to remove a a key from a specific
workspace. This `removeCache` function removes the key from the cache
and returns the object that was removed.
In the example below the array that was cached above is removed from the cache.
[source,text]
----
let(a=removeCache(workspace1, key1))
----
When this expression is sent to the `/stream` handler it responds with:
[source,json]
----
{
"result-set": {
"docs": [
{
"a": [
11,
22,
33
]
},
{
"EOF": true,
"RESPONSE_TIME": 0
}
]
}
}
----