---
name: projection-spec
description: Manage named field selection specifications that control which columns appear in a view , in what order , and how they are formatted or computed . Each projection captures a JSON serialized ProjectionField [ ] describing key , optional label , visibility , formatter , computed expression , and weight . Projections can be merged so that overlay fields win on key conflict and new fields are appended , and can be evaluated directly against a JSON row array to produce projected rows containing only the specified fields in the specified order
argument-hint: [command] [name] [fields]
allowed-tools: Read, Grep, Glob, Bash
---

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# ProjectionSpec

Manage named field selection specifications that control which columns appear in a view , in what order , and how they are formatted or computed . Each projection captures a JSON serialized ProjectionField [ ] describing key , optional label , visibility , formatter , computed expression , and weight . Projections can be merged so that overlay fields win on key conflict and new fields are appended , and can be evaluated directly against a JSON row array to produce projected rows containing only the specified fields in the specified order

## Commands

### create
Register a new named projection spec with the given field array . The fields 
 string is a JSON serialized ProjectionField [ ] where each entry may carry 
 key , label , visible , formatter , computed , and weight properties . An empty 
 array [ ] is valid and represents a zero field projection .

**Arguments:** `$0` **name** (string), `$1` **fields** (string)

### get
Return the projection spec identifier and its serialized field array for 
 the given name .

**Arguments:** `$0` **name** (string)

### merge
Combine two projection specs : overlay fields win on key conflict ( matching 
 by the key property ) , and fields present only in the overlay are appended 
 after the base fields . The resulting projection is stored under the name 
 base+overlay and its field array is returned .

**Arguments:** `$0` **base** (string), `$1` **overlay** (string)

### evaluate
Apply the named projection spec to a JSON serialized row array . Each row 
 is reduced to only the fields declared in the projection , in the order they 
 appear in the spec . Fields marked visible : false are excluded . The result 
 is a JSON serialized array of projected row objects .

**Arguments:** `$0` **name** (string), `$1` **rows** (string)

### list
Return a JSON serialized array of all registered projection spec names .