CsvAsyncQuery<T> class · CsvHelper

public sealed class CsvAsyncQuery<T> : IAsyncEnumerable<T>

Namespace: CsvHelper.Linq
Assembly: CsvHelper.Linq.dll
Implements: IAsyncEnumerable<T>
Builds: net10.0 netstandard2.1 netstandard2.0 net47
Source: CsvAsyncQuery.cs

Remarks

Its operators are instance methods, so they are chosen over the extension methods of the same names that Entity Framework Core and .NET 10's AsyncEnumerable have.

When the CSV reader runs the whole query (filters, skips and the operators that read the records it returns, such as Select and Take), the records stream; otherwise the records that the reader returns are read into memory first, and the rest of the query runs on them.

Methods

AllAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<bool> AllAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

Whether every result matches a condition; reading stops at the first that does not.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<bool>

true when all results match, or there are none.

Exceptions

ArgumentNullException: predicate is null.

AnyAsync(CancellationToken)

Added in v34.0.0

public Task<bool> AnyAsync(CancellationToken cancellationToken = default)

Whether the query has any result; reading stops at the first.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<bool>

true when there is a result.

AnyAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<bool> AnyAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

Whether any result matches a condition; reading stops at the first that does.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<bool>

true when a result matches.

Exceptions

ArgumentNullException: predicate is null.

CountAsync(CancellationToken)

Added in v34.0.0

public Task<int> CountAsync(CancellationToken cancellationToken = default)

Counts the results; the reader counts the records without reading their members when it can.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<int>

The number of results.

CountAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<int> CountAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

Counts the results that match a condition.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<int>

The number of results that match.

Exceptions

ArgumentNullException: predicate is null.

ElementAtAsync(int, CancellationToken)

Added in v34.0.0

public Task<T> ElementAtAsync(int index, CancellationToken cancellationToken = default)

The result at an index; the reader skips the records before it without reading their members when it can.

Parameters

indexint: The 0-based index.
cancellationTokenCancellationToken: Cancels the reading.

Returns

The result at index.

Exceptions

ArgumentOutOfRangeException: index is negative, or there are not that many results.

ExecuteAsync<TResult>(Expression<Func<IQueryable<T>, TResult>>, CancellationToken)

Added in v34.0.0

public Task<TResult> ExecuteAsync<TResult>(Expression<Func<IQueryable<T>, TResult>> operation, CancellationToken cancellationToken = default)

Runs any other operator that returns a single value, such as q => q.Sum(o => o.Total) or q => q.Max(o => o.Placed), reading the CSV asynchronously.

Type parameters

TResult: The type of the value.

Parameters

operationExpression<Func<IQueryable<T>, TResult>>: The operator, applied to the query.
cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<TResult>

The value.

Exceptions

ArgumentNullException: operation is null.

FirstAsync(CancellationToken)

Added in v34.0.0

public Task<T> FirstAsync(CancellationToken cancellationToken = default)

The first result.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

The first result.

Exceptions

InvalidOperationException: The query has no results.

FirstAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<T> FirstAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

The first result that matches a condition.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

The first result that matches.

Exceptions

ArgumentNullException: predicate is null.
InvalidOperationException: No result matches.

FirstOrDefaultAsync(CancellationToken)

Added in v34.0.0

public Task<T?> FirstOrDefaultAsync(CancellationToken cancellationToken = default)

The first result, or the default of T when there is none.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<T?>

The first result, or the default.

FirstOrDefaultAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<T?> FirstOrDefaultAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

The first result that matches a condition, or the default of T when none does.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<T?>

The first result that matches, or the default.

Exceptions

ArgumentNullException: predicate is null.

ForEachAsync(Action<T>, CancellationToken)

Added in v34.0.0

public Task ForEachAsync(Action<T> action, CancellationToken cancellationToken = default)

Runs the query and calls action with each result.

Parameters

actionAction<T>: What to do with each result.
cancellationTokenCancellationToken: Cancels the reading.

Returns

A task that completes after the last result.

Exceptions

ArgumentNullException: action is null.

GetAsyncEnumerator(CancellationToken)

Added in v34.0.0

public IAsyncEnumerator<T> GetAsyncEnumerator(CancellationToken cancellationToken = default)

Runs the query, reading the CSV asynchronously.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

IAsyncEnumerator<T>

An enumerator of the results; disposing it closes the sources it opened.

LastAsync(CancellationToken)

Added in v34.0.0

public Task<T> LastAsync(CancellationToken cancellationToken = default)

The last result.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

The last result.

Exceptions

InvalidOperationException: The query has no results.

LastOrDefaultAsync(CancellationToken)

Added in v34.0.0

public Task<T?> LastOrDefaultAsync(CancellationToken cancellationToken = default)

The last result, or the default of T when there is none.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<T?>

The last result, or the default.

LongCountAsync(CancellationToken)

Added in v34.0.0

public Task<long> LongCountAsync(CancellationToken cancellationToken = default)

Counts the results, as a long.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<long>

The number of results.

LongCountAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<long> LongCountAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

Counts the results that match a condition, as a long.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<long>

The number of results that match.

Exceptions

ArgumentNullException: predicate is null.

SingleAsync(CancellationToken)

Added in v34.0.0

public Task<T> SingleAsync(CancellationToken cancellationToken = default)

The only result.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

The only result.

Exceptions

InvalidOperationException: The query has no results, or more than one.

SingleAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<T> SingleAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

The only result that matches a condition.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

The only result that matches.

Exceptions

ArgumentNullException: predicate is null.
InvalidOperationException: No result matches, or more than one.

SingleOrDefaultAsync(CancellationToken)

Added in v34.0.0

public Task<T?> SingleOrDefaultAsync(CancellationToken cancellationToken = default)

The only result, or the default of T when there is none.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<T?>

The only result, or the default.

Exceptions

InvalidOperationException: The query has more than one result.

SingleOrDefaultAsync(Expression<Func<T, bool>>, CancellationToken)

Added in v34.0.0

public Task<T?> SingleOrDefaultAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default)

The only result that matches a condition, or the default of T when none does.

Parameters

predicateExpression<Func<T, bool>>: The condition.
cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<T?>

The only result that matches, or the default.

Exceptions

ArgumentNullException: predicate is null.
InvalidOperationException: More than one result matches.

ToArrayAsync(CancellationToken)

Added in v34.0.0

public Task<T[]> ToArrayAsync(CancellationToken cancellationToken = default)

Runs the query and returns its results in an array.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

Task<T[]>

The results.

ToListAsync(CancellationToken)

Added in v34.0.0

public Task<List<T>> ToListAsync(CancellationToken cancellationToken = default)

Runs the query and returns its results in a list.

Parameters

cancellationTokenCancellationToken: Cancels the reading.

Returns

The results.