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Gh-512: Document delete elements operation (#518)
* add docs on delete elements * add version * remove javadoc link
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‎docs/administration-guide/delete-elements.md

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# Delete Elements Operation
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In Gaffer 2.3.0 a DeleteElements operation was added to allow users
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to delete specific elements from their graph instance.
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!!! warning
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Deleting elements is not reversible. Use of this operation should be
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limited and users should run test a Operation Chain which extracts any elements
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to be deleted prior to running any delete operations.
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We will use the following graph to demonstrate how to delete elements from a
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Gaffer graph.
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```mermaid
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graph LR
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A(["Person
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ID: John"])
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--
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"Created
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weight: 0.2"
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-->
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B(["Software
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ID: 1"])
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A
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--
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"Created
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weight: 0.6"
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-->
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C(["Software
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ID: 2"])
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```
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To delete elements from a graph, users can simply add a `DeleteElements.Builder` to their
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Operation Chain. This will take as its input the output of any operations run prior to it.
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!!! example ""
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If a user gets the edge between John and Software 2 in a query and follows this
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up with a delete, then this edge will be removed leaving the three entities and a single edge.
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=== "Java"
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```java
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final OperationChain<Void> deleteElementsChain = new OperationChain.Builder()
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.first(new GetElements.Builder()
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.input(new EdgeSeed("John", "2", DirectedType.EITHER))
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.view(new View.Builder().edge("created").build())
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.build())
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.then(new DeleteElements())
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.build();
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graph.execute(deleteElementsChain, new User());
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```
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=== "JSON"
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```json
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{
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"class" : "OperationChain",
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"operations" : [{
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"class": "GetElements",
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"input": [{
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"class": "EdgeSeed",
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"source": "John",
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"destination": "2",
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"directedType": "EITHER"
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}],
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"view": {
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"edges": "created"
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}
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},
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{
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"class" : "DeleteElements"
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}]
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}
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```
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=== "Python"
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```python
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g.OperationChain(
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operations=[
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g.GetElements(
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input = [g.EdgeSeed(source="John", destination="2", directedType="Either")]
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view = g.ElementDefinition(group = "created")
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),
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g.DeleteElements()
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]
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)
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```
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Results:
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```JSON
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Entity[vertex="John",group="person"]
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Edge[source="John",destination="1",directed=true,matchedVertex=SOURCE,group="created",properties=Properties[weight=<java.lang.Float>0.2]]
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Entity[vertex="1",group="software"]
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Entity[vertex="2",group="software"]
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```
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If a user wishes to remove an entity and its associated edges, this is done by
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querying for that entity with no filters.
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!!! example ""
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If a user gets the John entity in a query and follows this up with a delete,
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then the John entity is removed and so are the edges for John -created-> 1
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and John-created-> 2.
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=== "Java"
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```java
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final OperationChain<Void> deleteElementsChain = new OperationChain.Builder()
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.first(new GetElements.Builder()
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.input(new EntitySeed("John"))
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.build())
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.then(new DeleteElements())
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.build();
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graph.execute(deleteElementsChain, new User());
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```
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=== "JSON"
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```json
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{
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"class" : "OperationChain",
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"operations" : [{
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"class": "GetElements",
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"input": [{
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"class": "EntitySeed",
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"vertex": "John"
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}]
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},
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{
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"class" : "DeleteElements"
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}
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]
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}
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```
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=== "Python"
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```python
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g.OperationChain(
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operations=[
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g.GetElements(
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input = [g.EntitySeed(vertex="John")]
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),
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g.DeleteElements()
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]
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)
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```
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Results:
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```JSON
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Entity[vertex="1",group="software"]
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Entity[vertex="2",group="software"]
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```
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If a user wishes to remove an entity but leave any associated, this is done by
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querying for that entity with a filter.
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!!! example ""
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If a user gets the John entity in a query but uses a `View` that filters for just entities, then the
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delete will leave the associated edges and only delete the John entity.
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=== "Java"
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```java
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final OperationChain<Void> deleteElementsChain = new OperationChain.Builder()
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.first(new GetElements.Builder()
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.input(new EntitySeed("John"))
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.view(new View.Builder().entity("person").build())
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.build())
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.then(new DeleteElements())
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.build();
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graph.execute(deleteElementsChain, new User());
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```
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=== "JSON"
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```json
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{
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"class" : "OperationChain",
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"operations" : [{
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"class": "GetElements",
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"input": [{
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"class": "EntitySeed",
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"vertex": "John"
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}],
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"view": {
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"entities": "person"
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}
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},
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{
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"class" : "DeleteElements"
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}
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]
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}
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```
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=== "Python"
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```python
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g.OperationChain(
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operations=[
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g.GetElements(
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input = [g.EdgeSeed(source="John", destination="2", directedType="Either")]
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view = g.ElementDefinition(group = "person")
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),
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g.DeleteElements()
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]
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)
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```
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Results:
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```JSON
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Edge[source="John",destination="1",directed=true,matchedVertex=SOURCE,group="created",properties=Properties[weight=<java.lang.Float>0.2]]
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Edge[source="John",destination="2",directed=true,matchedVertex=SOURCE,group="created",properties=Properties[weight=<java.lang.Float>0.6]]
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Entity[vertex="1",group="software"]
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Entity[vertex="2",group="software"]
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```

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