You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: create_table_template.rs
    path of file: ./repos/greptimedb/src/common/meta/src/ddl
    
    the code of the file until where you have to start completion: // Copyright 2023 Greptime Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::collections::HashMap;

use api::v1::region::{CreateRequest, RegionColumnDef};
use api::v1::{ColumnDef, CreateTableExpr, SemanticType};
use snafu::OptionExt;
use store_api::metric_engine_consts::LOGICAL_TABLE_METADATA_KEY;
use store_api::storage::{RegionId, RegionNumber};
use table::metadata::TableId;

use crate::error;
use crate::error::Result;
use crate::wal_options_allocator::prepare_wal_options;

pub(crate) fn build_template(create_table_expr: &CreateTableExpr) -> Result<CreateRequest> {
    let column_defs = create_table_expr
        .column_defs
        .iter()
        .enumerate()
        .map(|(i, c)| {
            let semantic_type = if create_table_expr.time_index == c.name {
                SemanticType::Timestamp
            } else if create_table_expr.primary_keys.contains(&c.name) {
                SemanticType::Tag
            } else {
                SemanticType::Field
            };

            RegionColumnDef {
                column_def: Some(ColumnDef {
                    name: c.name.clone(),
                    data_type: c.data_type,
                    is_null
    
pub(crate) fn build_template(create_table_expr: &CreateTableExpr) -> Result<CreateRequest> {
    let column_defs = create_table_expr
        .column_defs
        .iter()
        .enumerate()
        .map(|(i, c)| {
            let semantic_type = if create_table_expr.time_index == c.name {
                SemanticType::Timestamp
            } else if create_table_expr.primary_keys.contains(&c.name) {
                SemanticType::Tag
            } else {
                SemanticType::Field
            };

            RegionColumnDef {
                column_def: Some(ColumnDef {
                    name: c.name.clone(),
                    data_type: c.data_type,
                    is_nullable: c.is_nullable,
                    default_constraint: c.default_constraint.clone(),
                    semantic_type: semantic_type as i32,
                    comment: String::new(),
                    datatype_extension: c.datatype_extension.clone(),
                }),
                column_id: i as u32,
            }
        })
        .collect::<Vec<_>>();

    let primary_key = create_table_expr
        .primary_keys
        .iter()
        .map(|key| {
            column_defs
                .iter()
                .find_map(|c| {
                    c.column_def.as_ref().and_then(|x| {
                        if &x.name == key {
                            Some(c.column_id)
                        } else {
                            None
                        }
                    })
                })
                .context(error::PrimaryKeyNotFoundSnafu { key })
        })
        .collect::<Result<_>>()?;

    let template = CreateRequest {
        region_id: 0,
        engine: create_table_expr.engine.to_string(),
        column_defs,
        primary_key,
        path: String::new(),
        options: create_table_expr.table_options.clone(),
    };

    Ok(template)
}