What causes "type not supported yet" in MyCATApache/Mycat-Server?

Use Connection.createStatement() with no arguments, or pass ResultSet.TYPE_FORWARD_ONLY as the type.

MyCATApache/Mycat-Server · error · UnsupportedOperationException

type not supported yet

Error message

type not supported yet

What it means

The MongoStatement constructor validates the JDBC result-set type argument. The MongoDB backend only supports the default forward-only/read-only mode (type == ResultSet.TYPE_FORWARD_ONLY, i.e. 0); any other value (TYPE_SCROLL_INSENSITIVE = 1005, TYPE_SCROLL_SENSITIVE = 1004) throws UnsupportedOperationException('type not supported yet').

Solutions

Use Connection.createStatement() with no arguments, or pass ResultSet.TYPE_FORWARD_ONLY as the type.
Remove scrollable-result-set requests (last()/absolute()/previous() usage) and restructure code to iterate forward only.
If scrolling is required, buffer results in application memory after a forward-only fetch.
Patch MongoStatement to implement scrollable types if truly needed.

Example fix

// before
Statement st = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);

// after
Statement st = conn.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);

Defensive patterns

Strategy: validation

Validate before calling

if (resultSetType != ResultSet.TYPE_FORWARD_ONLY) {
    throw new IllegalArgumentException("MongoDB backend supports only TYPE_FORWARD_ONLY");
}

Try / catch

try {
    st = conn.createStatement(type, concur);
} catch (UnsupportedOperationException e) {
    if (e.getMessage().startsWith("type not supported")) {
        st = conn.createStatement(); // fall back to default forward-only
    } else {
        throw e;
    }
}

Prevention

Always create statements with the no-arg createStatement() on MongoDB connections.
Avoid scrollable result-set APIs (last/absolute/previous) in code that may run against MongoDB.
Centralize statement creation in one helper that pins FORWARD_ONLY.

When it happens

Trigger: Calling Connection.createStatement(resultSetType, resultSetConcurrency, resultSetHoldability) or createStatement(type, concurrency) with resultSetType != ResultSet.TYPE_FORWARD_ONLY on a MongoDB connection in MyCat.

Common situations: Frameworks or connection pools that request scrollable result sets by default (some ORM/DAO templates, GUI query tools, code migrated from a MySQL JDBC driver usage that used TYPE_SCROLL_INSENSITIVE).

Related errors

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/0fca4b2ee85637c1. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/backend/jdbc/mongodb/MongoStatement.java:34

public class MongoStatement implements Statement
{
	private MongoConnection _conn;
    private final int _type;
    private final int _concurrency;
    private final int _holdability;
    private int _fetchSize = 0;
    //int _maxRows = 0;
    private MongoResultSet _last;

    public MongoStatement(MongoConnection conn, int type, int concurrency, int holdability)
    {
        this._conn = conn;
        this._type = type;
        this._concurrency = concurrency;
        this._holdability = holdability;

        if (this._type != 0) {
			throw new UnsupportedOperationException("type not supported yet");
		}
        if (this._concurrency != 0) {
			throw new UnsupportedOperationException("concurrency not supported yet");
		}
        if (this._holdability != 0) {
			throw new UnsupportedOperationException("holdability not supported yet");
		}
    }

	@Override
	public <T> T unwrap(Class<T> iface) throws SQLException {
		
		throw new UnsupportedOperationException();//return null;
	}

	@Override
	public boolean isWrapperFor(Class<?> iface) throws SQLException {

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