Dictionaries - React Native SDK

Realm Object Models

You can define a dictionary of mixed values for a Realm object model in three ways:

• set the data type of your field to an empty object, "{}".

• Add the data type before the brackets to create a dictionary with values of a specific type. For example, "int{}" to specify that dictionary values must be integers or "string{}" to specify that dictionary values must be strings.

• Define the object type explicitly. This is necessary for using object Types in your Realm as ditionary values.

Realm disallows the use of . or $ characters in map keys. You can use percent encoding and decoding to store a map key that contains one of these disallowed characters.

// Percent encode . or $ characters to use them in map keys
const mapKey = "kitchen.windows";
const encodedMapKey = mapKey.replace(".", "%2E");

Create an Object with a Dictionary Value

In the following CreateHomeOwner example, we create a new object with a dictionary property.

The CreateHomeOwner component does the following:

• Create React state that represents the homeowner's name and address, respectively.

• Get access to an open realm instance by calling the useRealm() hook within the component.

• Create a component method SubmitHomeOwner() that performs a write transaction and creates a new HomeOwner object based on the TextInput values for the homeowner's name and address, respectively.

• Add an onPress event on the submit button that calls SubmitHomeOwner()

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const CreateHomeOwner = () => {
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  const [homeOwnerName, setHomeOwnerName] = useState('John Smith');
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  const [address, setAddress] = useState('1 Home Street');
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  const realm = useRealm();
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  const submitHomeOwner = () => {
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    // Create a HomeOwner realm object within a Write Transaction
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    realm.write(() => {
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      realm.create('HomeOwner', {
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        name: homeOwnerName,
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        // For the dictionary field, 'home', set the value
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        // to a regular JavaScript object
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        home: {
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          address,
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        },
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      });
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    });
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  };
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  return (
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    <View>
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      <TextInput
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        value={homeOwnerName}
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        onChangeText={text => setHomeOwnerName(text)}
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      />
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      <TextInput value={address} onChangeText={text => setAddress(text)} />
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      <Button
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        title='Submit Home Owner'
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        onPress={submitHomeOwner}
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      />
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    </View>
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  );
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};

Query for Objects with a Dictionary Property

To filter a query, run collection.filtered() to specify a subset of results based on the value(s) of one or more object properties. You can specify results based on the value of a dictionary's properties by using bracket notation.

You can also determine whether a results collection has a certain key or value by using <dictionary>.@keys or <dictionary>.@values. For instance, if you had a HomeOwner collection with a nested home dictionary, you could return all HomeOwner objects with a home with a "price" property by running the query: home.@keys = "price".

Update a Dictionary

Update a dictionary's property by using the dictionary.set() method or dot notation to set its property to a new value.

Delete Members of a Dictionary

To delete members of a dictionary, use the dictionary.remove() method with an array of properties to remove from the dictionary.