Interface IDuckDbVector<T>

Methods to retrieve items from DuckDB vectors.

Inherited Members

IDuckDbVector.IsItemValid(int)

IDuckDbVector.ValidityMask

IDuckDbVector.Length

IDuckDbVector.ColumnInfo

Namespace: Mallard

Assembly: Mallard.dll

Syntax

public interface IDuckDbVector<T> : IDuckDbVector where T : allows ref struct

Type Parameters

Name	Description
T

Remarks

This interface differs from IReadOnlyList<T> in two ways: firstly, there is dedicated handling of null values; and secondly, DuckDB vector readers are "ref structs" so they cannot implement enumerators without copying and converting element values to GC memory, which is obviously inefficient.

Methods

GetItem(int)

Retrieve a valid element of this vector.

Declaration

T GetItem(int index)

Parameters

Type	Name	Description
int	index	The index of the element to select.

Returns

Type	Description
T	The desired element of this vector.

Remarks

For the purposes of this method, an element that is missing in the DuckDB vector but is materialized as an instance of Nullable<T> is considered "valid", i.e. this method will not throw an exception.

(Otherwise, there would be no point in substituting a nullable value type for T. Consistency would argue that nullable reference types be treated the same way, but in .NET, reference nullability are only compiler-driven annotations and not part of the run-time type system, so an implementation of this interface generally cannot detect whether T is U or U? for reference types U. So, if T is a reference type, this method throws an exception if the source element in the DuckDB vector is missing.)

Clients that want to basically assume all the elements of the vector are valid would call this method.

Exceptions

Type	Condition
IndexOutOfRangeException	The index is out of range for the vector.
InvalidOperationException	The requested element is invalid.

GetItemOrDefault(int)

Retrieve an element of this vector, returning the default value if it is invalid.

Declaration

T? GetItemOrDefault(int index)

Parameters

Type	Name	Description
int	index	The index of the element to select.

Returns

Type	Description
T	The desired element of this vector.

Remarks

The "default" value refers to the default-initialized value of a variable of tyoe T.

Exceptions

Type	Condition
IndexOutOfRangeException	The index is out of range for the vector.

TryGetItem(int, out T)

Retrieve an element of this vector, or report that it is invalid.

Declaration

bool TryGetItem(int index, out T item)

Parameters

Type	Name	Description
int	index	The index of the element in this vector.
T	item	The item that is to be read out. Set to the element type's default value when the element is invalid.

Returns

Type	Description
bool	Whether the element is valid.

Exceptions

Type	Condition
IndexOutOfRangeException	The index is out of range for the vector.