【EFCORE笔记】元素操作&集合运算&转换类型

Enumerable.Zip

将指定函数应用于两个序列的对应元素，以生成结果序列。

Element Operations

Method Name	Description	More Information
ElementAt	Returns the element at a specified index in a collection.	Enumerable.ElementAt Queryable.ElementAt
ElementAtOrDefault	Returns the element at a specified index in a collection or a default value if the index is out of range.	Enumerable.ElementAtOrDefault Queryable.ElementAtOrDefault
First	Returns the first element of a collection, or the first element that satisfies a condition.	Enumerable.First Queryable.First
FirstOrDefault	Returns the first element of a collection, or the first element that satisfies a condition. Returns a default value if no such element exists.	Enumerable.FirstOrDefault Queryable.FirstOrDefault Queryable.FirstOrDefault<TSour ce>(IQueryable<TSource>)
Last	Returns the last element of a collection, or the last element that satisfies a condition.	Enumerable.Last Queryable.Last
LastOrDefault	Returns the last element of a collection, or the last element that satisfies a condition. Returns a default value if no such element exists.	Enumerable.LastOrDefault Queryable.LastOrDefault
Single	Returns the only element of a collection or the only element that satisfies a condition. Throws an InvalidOperationExceptionif there is no element or more than one element to return.	Enumerable.Single Queryable.Single
SingleOrDefault	Returns the only element of a collection or the only element that satisfies a condition. Returns a default value if there is no element to return. Throws an InvalidOperationException if there is more than one element to return.	Enumerable.SingleOrDefault Queryable.SingleOrDefault

Converting Data Types

Method Name	Description	More Information
AsEnumerable	Returns the input typed as IEnumerable<T>.	Enumerable.AsEnumerable

AsQueryable	Converts a (generic) IEnumerable to a (generic) IQueryable.	Queryable.AsQueryable
Cast	Casts the elements of a collection to a specified type.	Enumerable.Cast   Queryable.Cast
OfType	Filters values, depending on their ability to be cast to a specified type.	Enumerable.OfType   Queryable.OfType
ToArray	Converts a collection to an array. This method forces query execution.	Enumerable.ToArray
ToDictionary	Puts elements into a Dictionary<TKey,TValue> based on a key selector function. This method forces query execution.	Enumerable.ToDictionary
ToList	Converts a collection to a List<T>. This method forces query execution.	Enumerable.ToList
ToLookup	Puts elements into a Lookup<TKey,TElement> (a one-to- many dictionary) based on a key selector function. This method forces query execution.	Enumerable.ToLookup

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Enumerable.Zip

将指定函数应用于两个序列的对应元素，以生成结果序列。

Element Operations

Method Name	Description	More Information
ElementAt	Returns the element at a specified index in a collection.	Enumerable.ElementAt Queryable.ElementAt
ElementAtOrDefault	Returns the element at a specified index in a collection or a default value if the index is out of range.	Enumerable.ElementAtOrDefault Queryable.ElementAtOrDefault
First	Returns the first element of a collection, or the first element that satisfies a condition.	Enumerable.First Queryable.First
FirstOrDefault	Returns the first element of a collection, or the first element that satisfies a condition. Returns a default value if no such element exists.	Enumerable.FirstOrDefault Queryable.FirstOrDefault Queryable.FirstOrDefault<TSour ce>(IQueryable<TSource>)
Last	Returns the last element of a collection, or the last element that satisfies a condition.	Enumerable.Last Queryable.Last
LastOrDefault	Returns the last element of a collection, or the last element that satisfies a condition. Returns a default value if no such element exists.	Enumerable.LastOrDefault Queryable.LastOrDefault
Single	Returns the only element of a collection or the only element that satisfies a condition. Throws an InvalidOperationExceptionif there is no element or more than one element to return.	Enumerable.Single Queryable.Single
SingleOrDefault	Returns the only element of a collection or the only element that satisfies a condition. Returns a default value if there is no element to return. Throws an InvalidOperationException if there is more than one element to return.	Enumerable.SingleOrDefault Queryable.SingleOrDefault

Converting Data Types

Method Name	Description	More Information
AsEnumerable	Returns the input typed as IEnumerable<T>.	Enumerable.AsEnumerable

AsQueryable	Converts a (generic) IEnumerable to a (generic) IQueryable.	Queryable.AsQueryable
Cast	Casts the elements of a collection to a specified type.	Enumerable.Cast   Queryable.Cast
OfType	Filters values, depending on their ability to be cast to a specified type.	Enumerable.OfType   Queryable.OfType
ToArray	Converts a collection to an array. This method forces query execution.	Enumerable.ToArray
ToDictionary	Puts elements into a Dictionary<TKey,TValue> based on a key selector function. This method forces query execution.	Enumerable.ToDictionary
ToList	Converts a collection to a List<T>. This method forces query execution.	Enumerable.ToList
ToLookup	Puts elements into a Lookup<TKey,TElement> (a one-to- many dictionary) based on a key selector function. This method forces query execution.	Enumerable.ToLookup

Aggregation Operations

Method Name	Description	More Information
Aggregate	Performs a custom aggregation operation on the values of a collection.	Enumerable.Aggregate Queryable.Aggregate
Average	Calculates the average value of a collection of values.	Enumerable.Average Queryable.Average
Count	Counts the elements in a collection, optionally only those elements that satisfy a predicate function.	Enumerable.Count Queryable.Count
LongCount	Counts the elements in a large collection, optionally only those elements that satisfy a predicate function.	Enumerable.LongCount Queryable.LongCount
Max	Determines the maximum value in a collection.	Enumerable.Max Queryable.Max
Min	Determines the minimum value in a collection.	Enumerable.Min Queryable.Min
Sum	Calculates the sum of the values in a collection.	Enumerable.Sum Queryable.Sum