add support for coalesce in function calls

Author: lovasoa

CHANGELOG.md

@@ -33,6 +33,7 @@
 - Fix a bug where the `sqlpage.environment_variable` function would return an error if the environment variable was not set. Now it returns `null` instead.
 - Update ApexCharts to [v4.3.0](https://github.com/apexcharts/apexcharts.js/releases/tag/v4.3.0).
 - New `article` property in the text component to display text in a more readable, article-like format.
+- Add support for evaluating calls to `coalesce` inside sqlpage functions. This means you can now use `coalesce` inside arguments of sqlpage functions, and it will be evaluated inside sqlpage. For instance, this lets you call `sqlpage.link(coalesce($url, 'https://sql-page.com'))` to create a link that will use the value of `$url` if it is not null, or fallback to `https://sql-page.com` if it is null.
 
 ## 0.31.0 (2024-11-24)
 

src/webserver/database/sql.rs

@@ -659,6 +659,12 @@ fn expr_to_stmt_param(arg: &mut Expr) -> Option<StmtParam> {
                     json_obj_args.push(function_arg_to_stmt_param(arg)?);
                 }
                 Some(StmtParam::JsonArray(json_obj_args))
+            } else if func_name.eq_ignore_ascii_case("coalesce") {
+                let mut coalesce_args = Vec::with_capacity(args.len());
+                for arg in args {
+                    coalesce_args.push(function_arg_to_stmt_param(arg)?);
+                }
+                Some(StmtParam::Coalesce(coalesce_args))
             } else {
                 log::warn!("SQLPage cannot emulate the following function: {func_name}");
                 None

src/webserver/database/syntax_tree.rs

@@ -38,6 +38,7 @@ pub(crate) enum StmtParam {
     Literal(String),
     Null,
     Concat(Vec<StmtParam>),
+    Coalesce(Vec<StmtParam>),
     JsonObject(Vec<StmtParam>),
     JsonArray(Vec<StmtParam>),
     FunctionCall(SqlPageFunctionCall),
@@ -58,6 +59,13 @@ impl std::fmt::Display for StmtParam {
                 }
                 write!(f, ")")
             }
+            StmtParam::Coalesce(items) => {
+                write!(f, "COALESCE(")?;
+                for item in items {
+                    write!(f, "{item}, ")?;
+                }
+                write!(f, ")")
+            }
             StmtParam::JsonObject(items) => {
                 write!(f, "JSON_OBJECT(")?;
                 for item in items {
@@ -163,6 +171,7 @@ pub(super) async fn extract_req_param<'a, 'b>(
         StmtParam::Concat(args) => concat_params(&args[..], request, db_connection).await?,
         StmtParam::JsonObject(args) => json_object_params(&args[..], request, db_connection).await?,
         StmtParam::JsonArray(args) => json_array_params(&args[..], request, db_connection).await?,
+        StmtParam::Coalesce(args) => coalesce_params(&args[..], request, db_connection).await?,
         StmtParam::FunctionCall(func) => func.evaluate(request, db_connection).await.with_context(|| {
             format!(
                 "Error in function call {func}.\nExpected {:#}",
@@ -187,6 +196,19 @@ async fn concat_params<'a, 'b>(
     Ok(Some(Cow::Owned(result)))
 }
 
+async fn coalesce_params<'a, 'b>(
+    args: &[StmtParam],
+    request: &'a RequestInfo,
+    db_connection: &'b mut DbConn,
+) -> anyhow::Result<Option<Cow<'a, str>>> {
+    for arg in args {
+        if let Some(arg) = Box::pin(extract_req_param(arg, request, db_connection)).await? {
+            return Ok(Some(arg));
+        }
+    }
+    Ok(None)
+}
+
 async fn json_object_params<'a, 'b>(
     args: &[StmtParam],
     request: &'a RequestInfo,

tests/sql_test_files/it_works_coalesce_eval.sql

@@ -0,0 +1,5 @@
+select 'text' as component, 
+    case sqlpage.link(coalesce($i_do_not_exist, 'https://example.com'))
+        when 'https://example.com' then 'It works !'
+        else 'error: ' || coalesce(sqlpage.link(coalesce($i_do_not_exist, 'https://example.com')), 'NULL')
+    end AS contents;