Expose required array in custom MCP tool input schema

[Copilot]

Why make this change?

• Closes [Bug]: Custom tool inputSchema has empty properties #3399
• Custom MCP tools (DynamicCustomTool) build an inputSchema with typed properties from stored procedure metadata, but never emitted a JSON Schema required array. AI agents had no way to tell which parameters are mandatory and had to fall back to description text or describe_entities.

What is this change?

• DynamicCustomTool.BuildInputSchemaFromDbMetadata: collects parameter names while iterating SP parameters and adds a top-level required array when non-empty.
• DynamicCustomTool.BuildInputSchemaFromConfig (fallback path): same treatment for config-declared parameters.
• IsParameterRequired(bool? configuredRequired, bool hasDefault) helper centralizes the rule: a parameter is required unless config explicitly marks it optional (required: false) or supplies a default the engine applies when the caller omits it. Consistent with the execution-time default-application logic and describe_entities semantics.

Resulting schema:

"inputSchema": {
  "type": "object",
  "properties": { "productId": { "type": "integer" } },
  "required": [ "productId" ]
}

How was this tested?

• Integration Tests
• Unit Tests

DynamicCustomToolTests: required params listed, params with defaults / required:false excluded, zero-param SP omits the array, config-fallback path. DynamicCustomToolMsSqlIntegrationTests: validates required against live DB metadata (GetBook.id required; InsertBook defaulted params excluded; zero-param GetBooks omits the array).

Sample Request(s)

MCP tools/list response for a custom tool over get_book_by_id(@id int):

{
  "name": "get_book",
  "description": "Executes the get_book stored procedure",
  "inputSchema": {
    "type": "object",
    "properties": { "id": { "type": "integer", "description": "Parameter id" } },
    "required": [ "id" ]
  }
}

[Copilot]

Pull request overview

This pull request enhances MCP custom tool discoverability by emitting a JSON Schema required array in DynamicCustomTool input schemas, allowing agents/clients to distinguish mandatory parameters from optional/defaulted ones.

Changes:

• Add top-level required array emission to the DB-metadata schema path (BuildInputSchema) when at least one parameter is required.
• Add the same required array emission to the config-fallback schema path (BuildInputSchemaFromConfig).
• Add unit and MSSQL integration tests to validate required/optional/defaulted parameter behavior and the zero-parameter omission case.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs	Builds MCP tool inputSchema.required based on parameter requirement/default rules for both DB and config-fallback paths.
src/Service.Tests/Mcp/DynamicCustomToolTests.cs	Adds unit tests asserting required array inclusion/exclusion and omission for zero-parameter procedures, including config-fallback validation.
src/Service.Tests/Mcp/DynamicCustomToolMsSqlIntegrationTests.cs	Adds MSSQL integration coverage validating required against live stored procedure metadata and config defaults.

[Aniruddh25]

Here, this call to IsParameterRequired is not for config. the comment conveys config. Should be fixed to mention db metadata

[souvikghosh04]

@copilot please apply the suggesstion.

[Copilot]

Applied in 64cd204.

[Aniruddh25]

There should be a test for config defining defaults and also having the parameter specified as required. In this case, the parameter should still be present in the required array.

[souvikghosh04]

@copilot check if this is covered already or add this test.

[Copilot]

Added explicit config-fallback coverage in 0c38640. The new test verifies that a parameter with Required = true and a config default is excluded from inputSchema.required, matching the current default-application behavior.

[Aniruddh25]

Needs 1 more test for combination of required and default