What is the difference between IEnumerable and IQueryable?
💡 Concept: IEnumerable vs IQueryable
IEnumerable and IQueryable are interfaces used for querying data collections in C#, but they differ in execution and capabilities.
📘 Quick Intro
IEnumerable executes queries in memory and is suitable for in-memory collections, whereas IQueryable allows query translation for remote data sources like databases.
🧠 Analogy
Think of IEnumerable as reading a book already in your hands, while IQueryable is like sending a query to a librarian to fetch specific pages.
🔧 Technical Explanation
- 🧮 IEnumerable performs LINQ queries in-memory, after data is loaded.
- 🖥️ IQueryable translates LINQ queries to expressions executed on the data source.
- ⚙️ IQueryable supports deferred execution with query translation.
- 🔍 IEnumerable is suitable for collections; IQueryable for remote queries (e.g., databases).
- 💡 IQueryable can optimize queries and reduce data transferred.
🎯 Use Cases
- ✅ Use IEnumerable for local, in-memory collection filtering.
- ✅ Use IQueryable for querying databases and remote sources.
- ✅ IQueryable helps reduce data load by pushing filters to data source.
- ✅ Choose based on data source and performance needs.
💻 Code Example
using System;
using System.Collections.Generic;
using System.Linq;
class Program {
static void Main() {
List<int> numbers = new List<int> {1, 2, 3, 4, 5};
// IEnumerable example
IEnumerable<int> enumerable = numbers.Where(n => n > 2);
foreach (var num in enumerable) {
Console.WriteLine(num);
}
// IQueryable example with Entity Framework (example)
// IQueryable<int> queryable = dbContext.Numbers.Where(n => n > 2);
}
}
❓ Interview Q&A
Q1: Where does IEnumerable execute queries?
A: In memory after data is loaded.
Q2: What does IQueryable do?
A: Translates queries for remote execution.
Q3: Can IQueryable optimize queries?
A: Yes, by pushing filters to data source.
Q4: Is IEnumerable suitable for databases?
A: No, mainly for in-memory collections.
Q5: What is deferred execution?
A: Queries execute when enumerated.
Q6: Which namespace contains these interfaces?
A: System.Linq.
Q7: Can IQueryable cause performance gains?
A: Yes, by reducing data transfer.
Q8: What is the difference in query syntax?
A: IQueryable queries can be translated to SQL.
Q9: Can IEnumerable be used with LINQ?
A: Yes.
Q10: How to convert IQueryable to IEnumerable?
A: Using ToList() or AsEnumerable().
📝 MCQs
Q1. Where does IEnumerable execute queries?
- In memory
- Remote
- Database
- Server
Q2. What does IQueryable do?
- Executes locally
- Translates queries
- Deletes data
- Creates data
Q3. Can IQueryable optimize queries?
- No
- Yes
- Sometimes
- Never
Q4. Is IEnumerable suitable for databases?
- Yes
- No
- Sometimes
- Always
Q5. What is deferred execution?
- Queries execute immediately
- Queries execute when enumerated
- Queries never execute
- Queries are compiled
Q6. Namespace for IEnumerable and IQueryable?
- System.Collections
- System.Linq
- System.Text
- System.IO
Q7. Can IQueryable improve performance?
- No
- Yes
- Sometimes
- Never
Q8. Difference in query syntax?
- No difference
- IQueryable queries translate to SQL
- Only IEnumerable supports LINQ
- None
Q9. Can IEnumerable be used with LINQ?
- No
- Yes
- Sometimes
- Never
Q10. How to convert IQueryable to IEnumerable?
- ToArray()
- ToList() or AsEnumerable()
- Cast()
- Convert()
💡 Bonus Insight
Choosing between IEnumerable and IQueryable wisely improves performance and resource usage in LINQ queries.
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