Implementation:Lance format Lance Java ColumnAlteration

Knowledge Sources	Lance
Domains	Java_SDK, Dataset_Management
Last Updated	2026-02-08 19:33 GMT

Overview

Description

The ColumnAlteration class represents a set of modifications to apply to a specific column in a Lance dataset. It supports three types of alterations: renaming a column, changing its nullability, and casting it to a different Arrow data type. Each alteration is optional and identified by a column path string.

The class uses a builder pattern where the Builder constructor requires the column path. The builder directly modifies the internal ColumnAlteration instance's optional fields, making the build step lightweight. Multiple alterations can be combined on the same column in a single ColumnAlteration instance.

Usage

Use ColumnAlteration to alter existing columns in a Lance dataset schema. Combine multiple alterations (rename, nullable, cast) in one object for atomic application. This is typically submitted as part of a dataset alter-columns operation.

Code Reference

Source Location

java/src/main/java/org/lance/schema/ColumnAlteration.java

Signature

public class ColumnAlteration {
    public String getPath();
    public Optional<String> getRename();
    public Optional<Boolean> getNullable();
    public Optional<ArrowType> getDataType();

    public static class Builder {
        public Builder(String path);
        public Builder rename(String rename);
        public Builder nullable(boolean nullable);
        public Builder castTo(ArrowType dataType);
        public ColumnAlteration build();
    }
}

Import

import org.lance.schema.ColumnAlteration;

I/O Contract

Builder Inputs

Parameter	Type	Required	Description
path	String	Yes	The column path identifying the column to alter
rename	String	No	New name for the column
nullable	boolean	No	Whether the column should be nullable
castTo	ArrowType	No	Target Arrow data type for type casting

Outputs

Method	Return Type	Description
getPath()	String	The column path
getRename()	Optional<String>	The new column name, if set
getNullable()	Optional<Boolean>	The new nullability, if set
getDataType()	Optional<ArrowType>	The target data type for casting, if set

Usage Examples

// Rename a column
ColumnAlteration rename = new ColumnAlteration.Builder("old_name")
    .rename("new_name")
    .build();

// Make a column nullable
ColumnAlteration makeNullable = new ColumnAlteration.Builder("required_field")
    .nullable(true)
    .build();

// Cast a column to a different type
ColumnAlteration castType = new ColumnAlteration.Builder("score")
    .castTo(new ArrowType.FloatingPoint(FloatingPointPrecision.DOUBLE))
    .build();

// Combine multiple alterations on the same column
ColumnAlteration combined = new ColumnAlteration.Builder("amount")
    .rename("total_amount")
    .nullable(true)
    .castTo(new ArrowType.FloatingPoint(FloatingPointPrecision.DOUBLE))
    .build();

Related Pages

• Lance_format_Lance_Java_ProjectOp -- Changes schema without modifying data (column removal, reordering)
• Lance_format_Lance_Java_LanceField -- Lance field representation with type information
• Lance_format_Lance_Java_LanceSchema -- Lance schema containing fields and metadata