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description
ObjectBox queries help you quickly find objects matching criteria you've specified.

Queries

Using queries is simple: from your entity's Box, call Query() with conditions as arguments:

query := box.Query(Device_.Location.HasPrefix("US-", false))
devices, err := query.Find()

Building queries

The query in the code above uses a function HasPrefix on a device location. Where does this come from? ObjectBox generates a Device_ struct for you to reference available properties conveniently. This also allows code completion in your IDE and avoids typos: correctness is checked at compile time (string based queries would only be checked at run-time).

Let's say you have the following entity defined in your package:

type Device struct {
	Id       uint64
	Name     string
	Location string
	Profile  uint32
}

Using this input, the ObjectBox code generator creates a variable Device_ in the same package:

var Device_ = struct {
	Id       *objectbox.PropertyUint64
	Name     *objectbox.PropertyString
	Location *objectbox.PropertyString
	Profile  *objectbox.PropertyUint32
}{...}

You can use Device_ to construct type-specific conditions in place and combining them, forming the full query. The following example looks for devices located in the U. S. with profile number 42.

box.Query(Device_.Profile.Equals(42), Device_.Location.HasPrefix("US-", false))

{% hint style="info" %} If you frequently call the same query, you should cache the built query variable and re-use it. {% endhint %}

Notable conditions/operators

In addition to expected conditions like Equals(), NotEquals(), GreaterThan() and LessThan() there are also conditions like:

  • Between() to filter for values that are between the given two (inclusive)
  • In() and NotIn() to filter for values that match any in the given set,
  • HasPrefix(), HasSuffix() and Contains() for extended String filtering.

Working with query results

You have a few options how to handle the results of a query:

  • Find() returns a slice of the matching objects,
  • FindIds()fetches just the IDs of the matching objects as a slice, which can be more efficient in case you don't need the whole object,
  • Remove() deletes all the matching objects from the database (in a single transaction),
  • Count() gives you the number of the objects that match the query,
  • Describe() is a utility function which returns a human-readable representation of the query.

More to come

ObjectBox core can do much more with the queries, such as ordering, limits & offsets, setting parameters on reusable queries, aliases, etc. These are not yet supported by our Go API, but you can take a peek at https://docs.objectbox.io/queries to get the idea what's coming in the future releases.

Feel free to open a feature request on GitHub if you have an idea or a proposal.