How would you explain deferred execution in LINQ, especially when the query targets EF Core?

What is deferred execution in LINQ and EF Core?

Explains LINQ deferred execution with EF Core with practical .NET data-access examples and production trade-offs.

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TL;DR

Deferred execution means a LINQ query is not executed when it is defined. It runs when the results are enumerated, for example with ToListAsync, FirstOrDefaultAsync, AnyAsync, or a foreach. With EF Core, the query expression is translated to SQL at execution time. This lets me compose filters before hitting the database.

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Understanding of LINQ deferred execution with EF Core, EF Core/SQL behavior, API boundaries, production risks, and practical debugging or design judgment.

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Why this matters
Deferred execution determines when a LINQ query becomes SQL and runs. Misunderstanding that boundary can execute a query repeatedly, capture changed parameters, or move expensive work into an unexpected part of the request.
Deferred execution means a LINQ query is not executed when it is defined. It runs when the results are enumerated, for example with ToListAsync, FirstOrDefaultAsync, AnyAsync, or a foreach. With EF Core, the query expression is translated to SQL at execution time. This lets me compose filters before hitting the database.
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Details

Treating LINQ deferred execution with EF Core as a syntax detail instead of a production behavior.
Not checking generated SQL, query plans, or actual data volume.
Testing only with tiny local data and assuming production will behave the same.
Fixing symptoms with caching, timeouts, or retries before understanding the data-access cause.

How would you explain deferred execution in LINQ, especially when the query targets EF Core?

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