Firebase Queries and Indexing Fundamentals Quiz Quiz

Explore essential topics on Firebase queries and indexing with this easy quiz. Learn the basics of querying databases efficiently, applying filters, and understanding when and how to use indexes for optimal data retrieval.

1. Query Sorting

   Which method would you use to sort results in ascending order by a specific child property named 'score'?

   1. orderByKey('score')
   2. orderByChild('score')
   3. sortBy('score')
   4. orderByValue('score')

   Explanation: The correct method to sort data by the value of a specific child property is 'orderByChild('score')'. 'sortBy' is not a valid method for sorting in this context. 'orderByValue' sorts data by their value directly, not by the value of a child property. 'orderByKey' sorts data by their key, not by a property value.

2. Basic Filtering

   If you want to retrieve only records where the 'age' field equals 18, which query filter should you use?

   1. whereEqual(18)
   2. equalTo(18)
   3. onlyIf(age == 18)
   4. ageIs(18)

   Explanation: 'equalTo(18)' is the filter used to return only records where the 'age' field matches 18. 'whereEqual(18)' and 'ageIs(18)' are not valid filter methods in this query context. 'onlyIf(age == 18)' is incorrect because such syntax does not exist in this system.

3. Indexing Purpose

   What is the main benefit of adding an index to a field used in a query?

   1. Increases storage space
   2. Prevents duplicate entries
   3. Improves query performance and allows efficient data retrieval
   4. Ensures data is encrypted

   Explanation: Adding an index allows for faster and more efficient querying by reducing the time needed to search data. It does not encrypt data, so that option is incorrect. Indexing does not prevent duplicate entries nor does it aim to consume more storage; these are common misconceptions.

4. Index Warning Resolution

   If you receive an error stating that your query requires an index, what is the correct action to resolve it?

   1. Ignore the warning and run the query again
   2. Increase the database storage size
   3. Delete all existing indexes
   4. Add the suggested index definition to the index rules

   Explanation: The correct way to fix this issue is to add the provided index definition to the indexing rules as prompted. Deleting all indexes would make queries less efficient and is not a solution. Increasing storage has no impact on indexing. Ignoring the warning and retrying will not solve the root issue.

5. Query Limits

   Which method lets you limit the number of query results to the first 10 entries?

   1. limitToFirst(10)
   2. getFirst(10)
   3. takeFirst(10)
   4. fetchTop(10)

   Explanation: 'limitToFirst(10)' is the standard method to restrict results to the first 10 entries in the query's result set. 'takeFirst(10)', 'getFirst(10)', and 'fetchTop(10)' are not recognized query methods, and thus will not achieve the same outcome.

6. Order By Key

   What does the 'orderByKey()' function accomplish within a query?

   1. Groups data entries by type
   2. Sorts results by their keys in a defined order
   3. Limits the results to a numerical range
   4. Filters data by a specific property value

   Explanation: The function 'orderByKey()' arranges data entries based on their keys, enabling predictable ordering. It does not filter by property values, restrict data by value range, or group entries by type, so the other options are not applicable here.

7. Composite Index Requirement

   When is a composite index necessary for a query?

   1. When reading all data without filters
   2. When querying multiple fields together as filters or orderings
   3. When backing up the database
   4. When querying a single field only

   Explanation: Composite indexes are used when your query involves multiple fields, especially for complex filtering or sorting. If you only query a single field or read all data, a composite index is unnecessary. Creating backups does not require setting up composite indexes.

8. Query Filtering with Range

   Which pair of query methods would you use to fetch all entries where the 'score' is between 50 and 100?

   1. startAt(50) and endAt(100)
   2. limitToRange(50, 100)
   3. from(50) and to(100)
   4. beginWith(50) and finishAt(100)

   Explanation: 'startAt(50) and endAt(100)' are the standard filtering methods to select records within a specified range. The methods 'beginWith', 'finishAt', 'from', 'to', and 'limitToRange' are not valid in this context and will not produce the intended result.

9. Default Indexes

   Which field is always indexed by default in every data collection?

   1. No fields are indexed by default
   2. All string values in the collection
   3. The key (or identifier) of each data entry
   4. Every date field present

   Explanation: The primary key or unique identifier for each data entry is typically indexed by default, optimizing basic lookups. Not every string or date field gets indexed automatically. The option stating no fields are indexed contradicts standard practice.

10. Querying for Null Values

    How can you retrieve records where a certain child property is null or missing?

    1. Use orderByChild and equalTo(null)
    2. Specify 'missing' in the query
    3. Use filterNull() method
    4. Use notExists() function

    Explanation: To query for null or missing values of a child property, you must use 'orderByChild' in combination with 'equalTo(null)'. There is no 'notExists()' or 'filterNull()' function for this purpose, and specifying 'missing' as a parameter would not be recognized by the system.