Class DuckDbVectorDelegateReader

Provides access to a column of DuckDbResultChunk.

Inheritance

object

DuckDbVectorDelegateReader

Implements

IDuckDbVector

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: Mallard

Assembly: Mallard.dll

Syntax

public class DuckDbVectorDelegateReader : IDuckDbVector

Remarks

This type essentially provides the functionality of DuckDbVectorReader<T>, but without incorporating the vector element type as a generic parameter, and without the restrictions of "ref structs". It is necessary to fit some API shapes, in particular ADO.NET. Naturally, it has worse performance characteristics (in order to maintain the same level of memory safety), so DuckDbVectorReader<T> remains the preferred approach to reading DuckDB vectors.

The word "delegate" in the name of this type refers to its instances being like delegates (in the .NET sense of the term) to the chunk's column/vector.

Because the .NET type for the vector elements does not get specified (at construction), instances of this class assume the default type (mapping) as decided by this library.

Constructors

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DuckDbVectorDelegateReader(DuckDbResultChunk, int)

Obtains read access to a column (vector) in a result chunk coming from DuckDB.

Declaration

public DuckDbVectorDelegateReader(DuckDbResultChunk chunk, int columnIndex)

Parameters

Type	Name	Description
DuckDbResultChunk	chunk	The target chunk. To enforce memory safety (in the presence of potentially multi-threaded access), the chunk can no longer be explicitly disposed once any reference to a column is taken using this class. Subsequent calls to Dispose() will be silently ignored.
int	columnIndex	The index of the desired column. Must be between 0 (inclusive) and ColumnCount (exclusive).

Properties

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ColumnInfo

Information about the column that this vector is part of.

Declaration

public DuckDbColumnInfo ColumnInfo { get; }

Property Value

Type	Description
DuckDbColumnInfo

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ElementType

The .NET type that the elements in the DuckDB column are mapped to.

Declaration

public Type ElementType { get; }

Property Value

Type	Description
Type

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Length

The length (number of rows) inherited from the result chunk this vector is part of.

Declaration

public int Length { get; }

Property Value

Type	Description
int

Methods

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GetByteLength(int)

Get the length in bytes of a blob, string or bit string.

Declaration

public int GetByteLength(int rowIndex)

Parameters

Type	Name	Description
int	rowIndex	The (row) index of the element that is a blob, string or bit string.

Returns

Type	Description
int

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GetByteStream(int)

Get a read-only stream over the bytes of a blob, string, or bit string.

Declaration

public Stream GetByteStream(int rowIndex)

Parameters

Type	Name	Description
int	rowIndex	The (row) index of the element that is a blob, string or bit string.

Returns

Type	Description
Stream

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GetBytes(int, Span<byte>, out int, int)

Copy out a sub-span of bytes from a blob, string, or bit string.

Declaration

public int GetBytes(int rowIndex, Span<byte> destination, out int totalBytes, int offset = 0)

Parameters

Type	Name	Description
int	rowIndex	The (row) index of the element that is a blob, string or bit string.
Span<byte>	destination	Buffer where the bytes will be copied to.
int	totalBytes	The number of bytes that would be copied (given the same `offset`) if `destination` is big enough.
int	offset	The offset, measured in byte units from the beginning of the blob, string or bit string, to start copying from.

Returns

Type	Description
int	The number of bytes written to the beginning of `destination`.

Remarks

For a vector element that is a string, its byte content is the UTF-8 encoding of the string.

For a vector element that is a bit string, the byte content is the little-endian encoding as accepted by BitArray. (See also GetSegment(Span<byte>, int, int).

This method is primarily intended for implementing GetBytes(int, long, byte[], int, int).

Exceptions

Type	Condition
InvalidOperationException	The element type of this DuckDB vector is not a blob, string or bit string.

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GetChars(int, Span<char>, int)

Copy out a sub-span of UTF-16 code units from a string.

Declaration

public int GetChars(int rowIndex, Span<char> destination, int charOffset = 0)

Parameters

Type	Name	Description
int	rowIndex	The (row) index of the element that is a blob, string or bit string.
Span<char>	destination	Buffer where the bytes will be copied to.
int	charOffset	The offset, measured in UTF-16 code units from the beginning of the string to start copying from.

Returns

Type	Description
int	The number of UTF-16 code units written to the beginning of `destination`.

Remarks

This method is primarily intended for implementing GetChars(int, long, char[], int, int).

Exceptions

Type	Condition
InvalidOperationException	The element type of this DuckDB vector is not a string.

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GetObject(int)

Get an item in the vector, cast into object.

Declaration

public object GetObject(int rowIndex)

Parameters

Type	Name	Description
int	rowIndex	The (row) index of the element of the vector.

Returns

Type	Description
object

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GetObjectOrNull(int)

Get an item in the vector, cast into object, or null if the selected item is invalid.

Declaration

public object? GetObjectOrNull(int rowIndex)

Parameters

Type	Name	Description
int	rowIndex	The (row) index of the element of the vector.

Returns

Type	Description
object

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GetValue<T>(int)

Get an item in the vector in its default .NET type (without boxing it).

Declaration

public T GetValue<T>(int rowIndex)

Parameters

Type	Name	Description
int	rowIndex

Returns

Type	Description
T

Type Parameters

Name Description

Name	Description
T	The .NET type of the column, required to be specified since it has been "type-erased" from the type identity of this class. However, it must still match, at run-time, the actual type that the elements in the DuckDB column have been mapped to by default, as indicated by ElementType. (For reference types, a base class or interface can also match.) This type should not be a nullable value type; it would never match ElementType. There is no "notnull" constraint on `T` only because some APIs that would be implemented with this class do not have that shape.

The .NET type of the column, required to be specified since it has been "type-erased" from the type identity of this class. However, it must still match, at run-time, the actual type that the elements in the DuckDB column have been mapped to by default, as indicated by ElementType. (For reference types, a base class or interface can also match.)

This type should not be a nullable value type; it would never match ElementType. There is no "notnull" constraint on T only because some APIs that would be implemented with this class do not have that shape.

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IsItemValid(int)

Return whether an element of this vector is valid (not null).

Declaration

public bool IsItemValid(int index)

Parameters

Type	Name	Description
int	index	The index of the element of the vector.

Returns

Type	Description
bool	True if valid (non-null), false if invalid (null).

Exceptions

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

Implements

IDuckDbVector