C#: Missed FirstOrDefault query.

[michaelnebel]

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Missed opportunity to use FirstOrDefault

Programmers sometimes search a sequence by iterating over each element, testing it, and returning the first element that satisfies the test. If the loop completes without finding a match, the method then returns a default value such as null or default.

Recommendation

This pattern is directly available as the FirstOrDefault method in LINQ. Using the library method makes the search intent explicit and avoids manually spelling out the loop and fallback return.

Example

In this example the method searches a list of operations for the first operation with a matching identifier, returning null if no match is found.

usingSystem;usingSystem.Collections.Generic;classMissedFirstOrDefaultOpportunity{publicstaticOperationFindOperation(IEnumerable<Operation>operations,stringoperationId){foreach(varoperationinoperations){if(string.Equals(operation.OperationId,operationId,StringComparison.Ordinal))returnoperation;}returnnull;}}classOperation{publicstringOperationId{get;set;}}

The LINQ FirstOrDefault method can express this search more directly.

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;classMissedFirstOrDefaultOpportunityFix{publicstaticOperationFindOperation(IEnumerable<Operation>operations,stringoperationId){returnoperations.FirstOrDefault(operation =>string.Equals(operation.OperationId,operationId,StringComparison.Ordinal));}}

The following examples should not use FirstOrDefault, because they do more than return the matching element or because the fallback value is not the default value.

usingSystem;usingSystem.Collections.Generic;classMissedFirstOrDefaultOpportunityGood{publicstaticOperationFindOperationOrThrow(IEnumerable<Operation>operations,stringoperationId){foreach(varoperationinoperations){if(string.Equals(operation.OperationId,operationId,StringComparison.Ordinal))thrownewInvalidOperationException("Unexpected operation.");}returnnull;}publicstaticOperationFindReplacementOperation(IEnumerable<Operation>operations,stringoperationId){foreach(varoperationinoperations){if(string.Equals(operation.OperationId,operationId,StringComparison.Ordinal))returnoperation;}returnnewOperation();}publicstaticstringFindOperationId(IEnumerable<Operation>operations,stringoperationId){foreach(varoperationinoperations){if(string.Equals(operation.OperationId,operationId,StringComparison.Ordinal))returnoperation.OperationId;}returnnull;}}

References

• MSDN: Enumerable.FirstOrDefault Method.