Consulta de datos - React Native SDK

Filter with Full-Text Search

You can use Realm Query Language (RQL) to query on properties that have a Full-Text Search (FTS) index. To begin, use useQuery() to return the collection of realm objects you'd like to filter. To query the FTS indexed property for objects within the collection, use the TEXT predicate in your filtered query.

Exclude results for a word by placing the - character in front of the word. For example, a search for swan -lake would include all search results for swan excluding those with lake.

In the following example, we query on the Book.name field using the following Book object model:

class Book extends Realm.Object<Book> {
  name!: string;
  price?: number;
  static schema: ObjectSchema = {
    name: 'Book',
    properties: {
      name: {type: 'string', indexed: 'full-text'},
      price: 'int?',
    },
  };
}

import {useQuery} from "@realm/react";
// Retrieve book objects from realm
const books = useQuery(Book);
// Filter for books with 'hunger' in the name
const booksWithHunger = useQuery(Book, books => {
  return books.filtered('name TEXT $0', 'hunger');
});
// Filter for books with 'swan' but not 'lake' in the name
const booksWithSwanWithoutLake = useQuery(Book, books => {
  return books.filtered('name TEXT $0', 'swan -lake');
});

Operadores de comparación

The most straightforward operation in a search is to compare values. Realm Query Language has standard comparison operators like ==, >, >=, in, <, <=, and !=.

Para obtener documentación completa sobre los operadores de comparación, consulta la referencia de operadores de comparación del Realm Query Language.

The following example uses the query engine's comparison operators to:

• Find high priority tasks by comparing the value of the priority property value with a threshold number, above which priority can be considered high.

• Find just-started or short-running tasks by seeing if the progressMinutes property falls within a certain range.

• Find unassigned tasks by finding tasks where the assignee property is equal to null.

• Find tasks assigned to specific teammates Ali or Jamie by seeing if the assignee property is in a list of names.

const highPriorityTasks = tasks.filtered("priority > $0", 5);
const unassignedTasks = tasks.filtered("assignee == $0", null);
const lowProgressTasks = tasks.filtered("$0 <= progressMinutes && progressMinutes < $1", 1, 10);
const aliTasks = tasks.filtered("assignee == $0", "Ali");
console.log(
  `Number of high priority tasks: ${highPriorityTasks.length}`,
  `Number of unassigned tasks: ${unassignedTasks.length}`,
  `Number of just-started or short-running tasks: ${lowProgressTasks.length}`,
  `Number of tasks for Ali: ${aliTasks.length}`
);

Operadores lógicos

Create compound predicates using logical operators. Realm Query Language has standard logical operators like AND, OR, and NOT.

For complete documentation on logical operators, refer to the Realm Query Language logical operator reference.

El siguiente ejemplo utiliza los operadores lógicos de Realm Query Language para encontrar todas las tareas completadas de Ali. Encontramos todas las tareas donde el valor de la propiedad assignee es igual a 'Ali' Y el valor de la propiedad isComplete es true.

console.log(
  "Number of Ali's complete tasks: " +
    tasks.filtered("assignee == $0 && isComplete == $1", "Ali", true).length
);

Operadores de String

You can compare string values using string operators like ==, beginsWith, contains, and endsWith. You can also use the LIKE operator to search with regex-like wildcards.

For complete documentation on string operators, refer to the Realm Query Language string operator reference.

The following example uses Realm Query Language's string operators to find projects with a name starting with the letter 'e' and projects with names that contain 'ie'.

// Use [c] for case-insensitivity.
console.log(
  "Projects that start with 'e': " +
    projects.filtered("name BEGINSWITH[c] $0", 'e').length
);
console.log(
  "Projects that contain 'ie': " +
    projects.filtered("name CONTAINS $0", 'ie').length
);

Aggregate Operators

Recorre una colección y redúcela a un solo valor usando un operador de agregación.

For complete documentation on aggregate operators, refer to the Realm Query Language aggregate operator reference.

The following examples uses aggregate operators to show different facets of the data:

• @avg para mostrar proyectos con prioridad promedio de tareas superior a 5.

• @sum to show long running projects.

console.log(
  "Number of projects with average tasks priority above 5: " +
    projects.filtered("tasks.@avg.priority > $0", 5).length
);
console.log(
  "Number of long-running projects: " +
    projects.filtered("tasks.@sum.progressMinutes > $0", 120).length
);

Collection Operators

A collection operator uses rules to determine whether to pass each input collection object to the output collection by applying a given predicate to every element of a given list property of the object.

Para la documentación completa sobre operadores de recolección, consulta la referencia de operadores de colección de Realm Query Language.

The following examples uses Realm Query Language's collection operators to find:

• ALL for projects with no complete tasks.

• ANY for projects with any top priority tasks.

console.log(
  "Number of projects with no complete tasks: " +
    projects.filtered("ALL tasks.isComplete == $0", false).length
);
console.log(
  "Number of projects with any top priority tasks: " +
    projects.filtered("ANY tasks.priority == $0", 10).length
);