#642 - ENH: Add support for OneToMany expression isEmpty() / isNotEmpty() ... which is effectively an EXISTS and NOT EXISTS subquery

src/main/java/com/avaje/ebeaninternal/server/expression/IsEmptyExpression.java

@@ -0,0 +1,91 @@
+package com.avaje.ebeaninternal.server.expression;
+
+import com.avaje.ebeaninternal.api.HashQueryPlanBuilder;
+import com.avaje.ebeaninternal.api.ManyWhereJoins;
+import com.avaje.ebeaninternal.api.SpiExpression;
+import com.avaje.ebeaninternal.api.SpiExpressionRequest;
+import com.avaje.ebeaninternal.server.deploy.BeanDescriptor;
+import com.avaje.ebeaninternal.server.el.ElPropertyValue;
+import com.avaje.ebeaninternal.server.query.SplitName;
+
+import java.io.IOException;
+
+public class IsEmptyExpression extends AbstractExpression {
+
+  private final boolean empty;
+
+  private final String propertyPath;
+
+  public IsEmptyExpression(String propertyName, boolean empty) {
+    super(propertyName);
+    this.empty = empty;
+    this.propertyPath = SplitName.split(propertyName)[0];
+  }
+
+  @Override
+  public void writeDocQuery(DocQueryContext context) throws IOException {
+
+  }
+
+  public final String getPropName() {
+    return propName;
+  }
+
+  @Override
+  public void addBindValues(SpiExpressionRequest request) {
+    // no bind values
+  }
+
+  @Override
+  public void containsMany(BeanDescriptor<?> desc, ManyWhereJoins manyWhereJoin) {
+    // we don't want the extra join
+    propertyContainsMany(propertyPath, desc, manyWhereJoin);
+  }
+
+  @Override
+  public void addSql(SpiExpressionRequest request) {
+
+    ElPropertyValue prop = getElProp(request);
+    if (prop == null) {
+      throw new IllegalStateException("Property [" + propName + "] not found");
+    }
+
+    if (empty) {
+      request.append("not ");
+    }
+
+    request
+        .append("exists (select 1 from ")
+        .append(prop.getAssocIsEmpty(request, propertyPath))
+        .append(")");
+  }
+
+  /**
+   * Based on the type and propertyName.
+   */
+  @Override
+  public void queryPlanHash(HashQueryPlanBuilder builder) {
+    builder.add(IsEmptyExpression.class).add(propName);
+  }
+
+  @Override
+  public int queryBindHash() {
+    return 1;
+  }
+
+  @Override
+  public boolean isSameByPlan(SpiExpression other) {
+    if (!(other instanceof IsEmptyExpression)) {
+      return false;
+    }
+
+    IsEmptyExpression that = (IsEmptyExpression) other;
+    return this.propName.equals(that.propName)
+        && this.empty == that.empty;
+  }
+
+  @Override
+  public boolean isSameByBind(SpiExpression other) {
+    return (other instanceof IsEmptyExpression);
+  }
+}