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## org.neo4j.graphdb.index
Interface Index<T extends PropertyContainer>

Type Parameters:
  `T` - The type of entities this index manages. It may be either `Node`s or `Relationship`s.

All Superinterfaces:
  ReadableIndex<T>

All Known Subinterfaces:
  RelationshipIndex

    public interface Index<T extends PropertyContainer>

extends ReadableIndex<T>

An index to associate key/value pairs with entities (`Node`s or `Relationship`s) for fast lookup and querying. Any number of key/value pairs can be associated with any number of entities using `add(PropertyContainer, String, Object)` and dissociated with `remove(PropertyContainer, String, Object)`. Querting is done using `ReadableIndex.get(String, Object)` for exact lookups and `ReadableIndex.query(Object)` or `ReadableIndex.query(String, Object)` for more advanced querying, exposing querying capabilities from the backend which is backing this particular index. Write operations participates in transactions so committing and rolling back works the same way as usual in Neo4j.

Author:
  Mattias Persson

Method Summary
`void` | `add(T entity, String key, Object value)` Adds a key/value pair for `entity` to the index.
`void` | `delete()` Clears the index and deletes the configuration associated with it.
`T` | `putIfAbsent(T entity, String key, Object value)` Add the entity to this index for the given key/value pair if this particular key/value pair doesn't already exist.
`void` | `remove(T entity)` Removes an entity from the index and all its key/value pairs which has been previously associated using `add(PropertyContainer, String, Object)`.
`void` | `remove(T entity, String key)` Removes key/value pairs for `entity` where key is `key` from the index.
`void` | `remove(T entity, String key, Object value)` Removes a key/value pair for `entity` from the index.

Methods inherited from interface org.neo4j.graphdb.index.ReadableIndex
`get, getEntityType, getGraphDatabase, getName, isWriteable, query, query`

Method Detail

### add

    void add(T entity,
             String key,
             Object value)

  Adds a key/value pair for `entity` to the index. If that key/value pair for the entity is already in the index it's up to the implementation to make it so that such an operation is idempotent.

  Parameters:
    `entity` - the entity (i.e `Node` or `Relationship`) to associate the key/value pair with.
    `key` - the key in the key/value pair to associate with the entity.
    `value` - the value in the key/value pair to associate with the entity.

### remove

    void remove(T entity,
                String key,
                Object value)

  Removes a key/value pair for `entity` from the index. If that key/value pair isn't associated with `entity` in this index this operation doesn't do anything.

  Parameters:
    `entity` - the entity (i.e `Node` or `Relationship`) to dissociate the key/value pair from.
    `key` - the key in the key/value pair to dissociate from the entity.
    `value` - the value in the key/value pair to dissociate from the entity.

### remove

    void remove(T entity,
                String key)

  Removes key/value pairs for `entity` where key is `key` from the index. Implementations can choose to not implement this method and should in that case throw `UnsupportedOperationException`.

  Parameters:
    `entity` - the entity (`Node` or `Relationship`) to remove the this index.

### remove

    void remove(T entity)

  Removes an entity from the index and all its key/value pairs which has been previously associated using `add(PropertyContainer, String, Object)`. Implementations can choose to not implement this method and should in that case throw `UnsupportedOperationException`.

  Parameters:
    `entity` - the entity (`Node` or `Relationship`) to remove the this index.

### delete

    void delete()

  Clears the index and deletes the configuration associated with it. After this it's invalid to call any other method on this index. However if the transaction which the delete operation was called in gets rolled back it again becomes ok to use this index.

### putIfAbsent

    T putIfAbsent(T entity,
                  String key,
                  Object value)

  Add the entity to this index for the given key/value pair if this particular key/value pair doesn't already exist. This ensures that only one entity will be associated with the key/value pair even if multiple transactions are trying to add it at the same time. One of those transactions will win and add it while the others will block, waiting for the winning transaction to finish. If the winning transaction was successful these other transactions will return the associated entity instead of adding it. If it wasn't successful the waiting transactions will begin a new race to add it.

  Parameters:
    `entity` - the entity (i.e `Node` or `Relationship`) to associate the key/value pair with.
    `key` - the key in the key/value pair to associate with the entity.
    `value` - the value in the key/value pair to associate with the entity.
  Returns:
    the previously indexed entity, or `null` if no entity was indexed before (and the specified entity was added to the index).

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