com.googlecode.objectify.cmd

Interface SimpleQuery<T>

All Superinterfaces:

Iterable<T>, QueryExecute<T>, com.google.appengine.api.datastore.QueryResultIterable<T>

All Known Subinterfaces:

Loader, LoadType<T>, Query<T>

All Known Implementing Classes:

LoaderImpl, QueryImpl, SimpleQueryImpl

public interface SimpleQuery<T>
extends QueryExecute<T>

A restricted set of query operations that apply to both kindless queries and typed queries.

Author:

Jeff Schnitzer

Method Summary

Modifier and Type	Method and Description
SimpleQuery<T>	ancestor(Object keyOrEntity) Restricts result set only to objects which have the given ancestor somewhere in the chain.
SimpleQuery<T>	chunk(int value) Sets the internal chunking and prefetching strategy within the low-level API.
SimpleQuery<T>	chunkAll() Sets the internal chunking and prefetching strategy within the low-level API to attempt to get all results at once.
int	count() Count the total number of values in the result.
SimpleQuery<T>	distinct(boolean value) Determines whether this is a SELECT DISTINCT query.
SimpleQuery<T>	endAt(com.google.appengine.api.datastore.Cursor value) Ends query results at the specified Cursor.
SimpleQuery<T>	filterKey(Object value) An alias for filterKey("=", value)
SimpleQuery<T>	filterKey(String condition, Object value) Create a filter on the key of an entity.
SimpleQuery<T>	hybrid(boolean force) This method forces Objectify to (or not to) hybridize the query into a keys-only fetch plus batch get.
QueryKeys<T>	keys() Switches to a keys-only query.
SimpleQuery<T>	limit(int value) Limit the fetched result set to a certain number of values.
SimpleQuery<T>	offset(int value) Starts the query results at a particular zero-based offset.
SimpleQuery<T>	orderKey(boolean descending) Orders results by the key.
SimpleQuery<T>	project(String... fields) Converts this query into a projection query.
SimpleQuery<T>	reverse() Reverse the query, as described in the GAE docs.
SimpleQuery<T>	startAt(com.google.appengine.api.datastore.Cursor value) Starts query results at the specified Cursor.
String	toString() Generates a string that consistently and uniquely specifies this query.

Methods inherited from interface com.googlecode.objectify.cmd.QueryExecute

first, iterable, list

Methods inherited from interface com.google.appengine.api.datastore.QueryResultIterable

iterator

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Method Detail

filterKey

SimpleQuery<T> filterKey(String condition,
                         Object value)

Create a filter on the key of an entity. Examples:

• filterKey(">=", key) (standard inequalities)
• filterKey("=", key) (wouldn't you rather do a load-by-key?)
• filterKey("", key) (if no operator, = is assumed)
• filterKey("!=", key)
• filterKey("in", keyList) (wouldn't you rather do a batch load-by-key?)

The key parameter can be anything key-ish; a Key, a native datastore key, a Ref, a pojo entity, etc.

See the Google documentation for indexes for an explanation of what you can and cannot filter for.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Returns:

a new immutable query object that applies the filter

filterKey

SimpleQuery<T> filterKey(Object value)

An alias for filterKey("=", value)

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Returns:

a new immutable query object that applies the filter

orderKey

SimpleQuery<T> orderKey(boolean descending)

Orders results by the key.

Parameters:

descending - if true, specifies a descending (aka reverse) sort

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Returns:

a new immutable query object that applies the sort order

ancestor

SimpleQuery<T> ancestor(Object keyOrEntity)

Restricts result set only to objects which have the given ancestor somewhere in the chain. Doesn't need to be the immediate parent. The specified ancestor itself will be included in the result set (if it exists).

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Parameters:

keyOrEntity - can be a Key, a Key, or an Objectify entity object.

Returns:

a new immutable query object that applies the ancestor filter

limit

SimpleQuery<T> limit(int value)

Limit the fetched result set to a certain number of values.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Parameters:

value - must be >= 0. A value of 0 indicates no limit.

Returns:

a new immutable query object that applies the limit

offset

SimpleQuery<T> offset(int value)

Starts the query results at a particular zero-based offset. This can be extraordinarily expensive because each skipped entity is billed as a "minor datastore operation". If you can, you probably want to use cursors instead.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Parameters:

value - must be >= 0

Returns:

a new immutable query object that applies the offset

startAt

SimpleQuery<T> startAt(com.google.appengine.api.datastore.Cursor value)

Starts query results at the specified Cursor. You can obtain a Cursor from a QueryResultIterator by calling the getCursor() method.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Note that limit() and offset() are NOT encoded within a cursor; they operate on the results of the query after a cursor is established.

Returns:

a new immutable query object that applies the cursor

endAt

SimpleQuery<T> endAt(com.google.appengine.api.datastore.Cursor value)

Ends query results at the specified Cursor. You can obtain a Cursor from a QueryResultIterator by calling the getCursor() method.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Note that limit() and offset() are NOT encoded within a cursor; they operate on the results of the query after a cursor is established.

Returns:

a new immutable query object that applies the cursor

chunk

SimpleQuery<T> chunk(int value)

Sets the internal chunking and prefetching strategy within the low-level API. Affects performance only; the result set will be the same.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Parameters:

value - must be >= 0

Returns:

a new immutable query object that applies the chunk size

chunkAll

SimpleQuery<T> chunkAll()

Sets the internal chunking and prefetching strategy within the low-level API to attempt to get all results at once. Affects performance only; the result set will be the same.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Same as chunk(Integer.MAX_VALUE).

Returns:

a new immutable query object that applies the chunk size

project

SimpleQuery<T> project(String... fields)

Converts this query into a projection query. Projection queries allow values to be selected directly out of an index rather than loading the whole entity. While this allows data to be fetched quickly and cheaply, it is limited to selecting data that exists in an index.

Entities returned from projection queries are NOT kept in the session cache. However, @Load annotations are processed normally.

This method can be called more than once; it will have the same effect as passing all the fields in to a single call.

Parameters:

fields - is one or more field names

Returns:

a new immutable query object that projects the specified fields

distinct

SimpleQuery<T> distinct(boolean value)

Determines whether this is a SELECT DISTINCT query.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Returns:

a new immutable query object that applies the distinct operator

reverse

SimpleQuery<T> reverse()

Reverse the query, as described in the GAE docs.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Returns:

a new immutable query object that reverses the order of results

hybrid

SimpleQuery<T> hybrid(boolean force)

This method forces Objectify to (or not to) hybridize the query into a keys-only fetch plus batch get.

If Objectify knows you are fetching an entity type that can be cached, it automatically converts queries into a "hybrid" of keys-only query followed by a batch fetch of the keys. This is cheaper (keys-only results are 1/7th the price of a full fetch) and, if the cache hits, significantly faster. However, there are some circumstances in which you may wish to force behavior one way or another:

• Issuing a kindless query (which Objectify will not auto-hybridize) when you know a significant portion of the result set is cacheable.
• Some exotic queries cannot be made keys-only, and produce an exception from the Low-Level API when you try to execute the query. Objectify tries to detect these cases but since the underlying implementation may change, you may need to force hybridization off in some cases.
• Hybrid queries have a slightly different consistency model than normal queries. You may wish to force hybridization off to ensure a weakly consistent query (see below).

For the most part, hybridization only affects the performance and cost of queries. However, it is possible for hybridization to alter the content of the result set. In the HRD, queries always have EVENTUAL consistency but get operations may have either STRONG or EVENTUAL consistency depending on the read policy (see Objectify.consistency(). The keys-only query results will always be EVENTUAL and may return data that has been deleted, but Objectify will exclude these results when the more-current batch get fails to return data. So the count of the returned data may actually be less than the limit(), even if there are plenty of actual results. hybrid(false) will prevent this behavior.

Note that in hybrid queries, the chunk size defines the batch size.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Returns:

a new immutable query object that forces hybridization on or off

keys

QueryKeys<T> keys()

Switches to a keys-only query. Keys-only responses are billed as "minor datastore operations" which are faster and free compared to fetching whole entities.

All command objects are immutable; this method returns a new object instead of modifying the current command object.

Returns:

a new immutable query object that returns keys rather than whole entities

count

int count()

Count the total number of values in the result. limit and offset are obeyed. This is somewhat faster than fetching, but the time still grows with the number of results. The datastore actually walks through the result set and counts for you.

Immediately executes the query; there is no async version of this method.

WARNING: Each counted entity is billed as a "datastore minor operation". Even though these are free, they may take significant time because they require an index walk.

toString

String toString()

Generates a string that consistently and uniquely specifies this query. There is no way to convert this string back into a query and there is no guarantee that the string will be consistent across versions of Objectify.

In particular, this value is useful as a key for a simple memcache query cache.

Specified by:

toString in interface QueryExecute<T>

Overrides:

toString in class Object