addressed the review comments

Author: banrovegrie

docs/docs/core/flow_def.mdx

@@ -313,7 +313,7 @@ Types of the fields must be key types. See [Key Types](data_types#key-types) for
 
     *   `field_name`: the field to create vector index.
     *   `metric`: the similarity metric to use.
-    *   `method`: the index algorithm and optional tuning parameters. Defaults to HNSW. Use `cocoindex.HnswVectorIndexMethod()` or `cocoindex.IvfFlatVectorIndexMethod()` to customize the method and its parameters.
+    *   `method` (optional): the index algorithm and optional tuning parameters. Leave unset to use the target default (HNSW for Postgres). Use `cocoindex.HnswVectorIndexMethod()` or `cocoindex.IvfFlatVectorIndexMethod()` to customize the method and its parameters.
 
 #### Similarity Metrics
 

python/cocoindex/index.py

@@ -1,5 +1,5 @@
 from enum import Enum
-from dataclasses import dataclass, field
+from dataclasses import dataclass
 from typing import Sequence, Union
 
 
@@ -13,7 +13,7 @@ class VectorSimilarityMetric(Enum):
 class HnswVectorIndexMethod:
     """HNSW vector index parameters."""
 
-    type: str = field(init=False, default="hnsw")
+    kind: str = "Hnsw"
     m: int | None = None
     ef_construction: int | None = None
 
@@ -22,7 +22,7 @@ class HnswVectorIndexMethod:
 class IvfFlatVectorIndexMethod:
     """IVFFlat vector index parameters."""
 
-    type: str = field(init=False, default="ivfflat")
+    kind: str = "IvfFlat"
     lists: int | None = None
 
 
@@ -37,7 +37,7 @@ class VectorIndexDef:
 
     field_name: str
     metric: VectorSimilarityMetric
-    method: VectorIndexMethod = field(default_factory=HnswVectorIndexMethod)
+    method: VectorIndexMethod | None = None
 
 
 @dataclass

src/base/spec.rs

@@ -385,7 +385,7 @@ impl fmt::Display for VectorSimilarityMetric {
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
-#[serde(tag = "type", rename_all = "snake_case")]
+#[serde(tag = "kind")]
 pub enum VectorIndexMethod {
     Hnsw {
         #[serde(default, skip_serializing_if = "Option::is_none")]
@@ -399,20 +399,11 @@ pub enum VectorIndexMethod {
     },
 }
 
-impl Default for VectorIndexMethod {
-    fn default() -> Self {
-        Self::Hnsw {
-            m: None,
-            ef_construction: None,
-        }
-    }
-}
-
 impl VectorIndexMethod {
     pub fn kind(&self) -> &'static str {
         match self {
-            Self::Hnsw { .. } => "hnsw",
-            Self::IvfFlat { .. } => "ivfflat",
+            Self::Hnsw { .. } => "Hnsw",
+            Self::IvfFlat { .. } => "IvfFlat",
         }
     }
 
@@ -439,16 +430,16 @@ impl fmt::Display for VectorIndexMethod {
                     parts.push(format!("ef_construction={}", ef));
                 }
                 if parts.is_empty() {
-                    write!(f, "hnsw")
+                    write!(f, "Hnsw")
                 } else {
-                    write!(f, "hnsw({})", parts.join(","))
+                    write!(f, "Hnsw({})", parts.join(","))
                 }
             }
             Self::IvfFlat { lists } => {
                 if let Some(lists) = lists {
-                    write!(f, "ivfflat(lists={lists})")
+                    write!(f, "IvfFlat(lists={lists})")
                 } else {
-                    write!(f, "ivfflat")
+                    write!(f, "IvfFlat")
                 }
             }
         }
@@ -459,16 +450,18 @@ impl fmt::Display for VectorIndexMethod {
 pub struct VectorIndexDef {
     pub field_name: FieldName,
     pub metric: VectorSimilarityMetric,
-    #[serde(default)]
-    pub method: VectorIndexMethod,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub method: Option<VectorIndexMethod>,
 }
 
 impl fmt::Display for VectorIndexDef {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        if self.method.is_default() {
-            write!(f, "{}:{}", self.field_name, self.metric)
-        } else {
-            write!(f, "{}:{}:{}", self.field_name, self.metric, self.method)
+        match &self.method {
+            None => write!(f, "{}:{}", self.field_name, self.metric),
+            Some(method) if method.is_default() => {
+                write!(f, "{}:{}", self.field_name, self.metric)
+            }
+            Some(method) => write!(f, "{}:{}:{}", self.field_name, self.metric, method),
         }
     }
 }

src/ops/targets/postgres.rs

@@ -461,24 +461,24 @@ fn to_vector_similarity_metric_sql(metric: VectorSimilarityMetric) -> &'static s
 }
 
 fn to_index_spec_sql(index_spec: &VectorIndexDef) -> Cow<'static, str> {
-    let method = match &index_spec.method {
-        spec::VectorIndexMethod::Hnsw { .. } => "hnsw",
-        spec::VectorIndexMethod::IvfFlat { .. } => "ivfflat",
-    };
-    let options = match &index_spec.method {
-        spec::VectorIndexMethod::Hnsw { m, ef_construction } => {
+    let (method, options) = match index_spec.method.as_ref() {
+        Some(spec::VectorIndexMethod::Hnsw { m, ef_construction }) => {
             let mut opts = Vec::new();
             if let Some(m) = m {
                 opts.push(format!("m = {}", m));
             }
             if let Some(ef) = ef_construction {
                 opts.push(format!("ef_construction = {}", ef));
             }
-            opts
+            ("hnsw", opts)
         }
-        spec::VectorIndexMethod::IvfFlat { lists } => lists
-            .map(|lists| vec![format!("lists = {}", lists)])
-            .unwrap_or_default(),
+        Some(spec::VectorIndexMethod::IvfFlat { lists }) => (
+            "ivfflat",
+            lists
+                .map(|lists| vec![format!("lists = {}", lists)])
+                .unwrap_or_default(),
+        ),
+        None => ("hnsw", Vec::new()),
     };
     let with_clause = if options.is_empty() {
         String::new()
@@ -501,9 +501,9 @@ fn to_vector_index_name(table_name: &str, vector_index_def: &spec::VectorIndexDe
         vector_index_def.field_name,
         to_vector_similarity_metric_sql(vector_index_def.metric)
     );
-    if !vector_index_def.method.is_default() {
+    if let Some(method) = vector_index_def.method.as_ref().filter(|m| !m.is_default()) {
         name.push_str("__");
-        name.push_str(vector_index_def.method.kind());
+        name.push_str(&method.kind().to_ascii_lowercase());
     }
     name
 }