59 lines
1.8 KiB
Markdown
59 lines
1.8 KiB
Markdown
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The Realm JavaScript SDK supports querying based on a language inspired by [NSPredicate](https://realm.io/news/nspredicate-cheatsheet/).
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The {@link Realm.Collection#filtered Collection.filtered()} method is used to query a Realm:
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```JS
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let contacts = realm.objects('Contact');
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let friendsPage2 = contacts.filtered('type == "friend" AND name BEGINSWITH "B"');
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```
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It's possible to filter by linked or child objects with a keypath.
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Example:
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```JS
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let johnsChildren = realm.Object('Contact').filtered('father.name == "John"');
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```
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Query strings can use numbered (`$0`, `$1`, ...) placeholders. The succeeding parameters contain the values.
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Named placeholders are **not** yet supported.
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Example:
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```JS
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let merlots = wines.filtered('variety == $0 && vintage <= $1', 'Merlot', maxYear);
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```
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### Relational operators
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You can use equality comparison on all property types:
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`==` and `!=`
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Furthermore, the following can be used on numerical types:
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`<`, `<=`, `>`, `>=`
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Example:
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```JS
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let oldContacts = realm.objects('Contact').filtered('age > 2');
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```
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Note that for boolean properties, you should test against the expected keyword.
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Example:
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```JS
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let women = realm.objects('Contact').filtered('isMale == false');
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```
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### String operators
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For string properties, prefix, suffix, and substring queries are supported by using the `BEGINSWITH`, `ENDSWITH`, and `CONTAINS` operators.
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For any string operation you can append `[c]` to the operator to make it case insensitive.
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Example:
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```JS
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let peopleWhoseNameContainsA = realm.objects('Contact').filtered('name CONTAINS[c] "a"');
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let Johns = realm.objects('Contact').filtered('name ==[c] "john"');
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```
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### Composition
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Use parentheses and the `&&`/`AND` and `||`/`OR` operators to compose queries. You can negate a predicate with `!`/`NOT`.
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