#1297 - ENH: Add DtoQuery ... such that we can map native SQL queries automatically into "DTO beans"

src/main/java/io/ebeaninternal/server/dto/DtoMeta.java

@@ -0,0 +1,119 @@
+package io.ebeaninternal.server.dto;
+
+import java.util.Arrays;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Holds property and constructor meta data for a given DTO bean type.
+ *
+ * Uses this to map a mapping request (columns) to a 'query plan' (constructor and setters).
+ */
+class DtoMeta {
+
+  private final Class<?> dtoType;
+  private final Map<String, DtoMetaProperty> propMap = new LinkedHashMap<>();
+
+  private final Map<Integer, DtoMetaConstructor> constructorMap = new LinkedHashMap<>();
+
+  private final DtoMetaConstructor defaultConstructor;
+  private final DtoMetaConstructor maxArgConstructor;
+
+  DtoMeta(Class<?> dtoType, List<DtoMetaConstructor> constructors, List<DtoMetaProperty> properties) {
+    this.dtoType = dtoType;
+
+    for (DtoMetaProperty property : properties) {
+      propMap.put(property.getName().toUpperCase(), property);
+    }
+
+    int maxArg = 0;
+
+    DtoMetaConstructor defaultConstructor = null;
+    DtoMetaConstructor maxArgConstructor = null;
+
+    for (DtoMetaConstructor constructor : constructors) {
+      int args = constructor.getArgCount();
+      constructorMap.put(args, constructor);
+      if (args == 0) {
+        defaultConstructor = constructor;
+      } else if (args > maxArg) {
+        maxArgConstructor = constructor;
+        maxArg = args;
+      }
+    }
+    this.defaultConstructor = defaultConstructor;
+    this.maxArgConstructor = maxArgConstructor;
+  }
+
+  public DtoQueryPlan match(DtoMappingRequest request) {
+
+    DtoColumn[] cols = request.getColumnMeta();
+
+    int colLen = cols.length;
+    DtoMetaConstructor constructor = constructorMap.get(colLen);
+    if (constructor != null) {
+      return new DtoQueryPlanConstructor(request, constructor);
+    }
+    if (maxArgConstructor != null && colLen > maxArgConstructor.getArgCount()) {
+      // maxArgConst + setters
+      return matchMaxArgPlusSetters(request);
+    }
+    if (defaultConstructor != null) {
+      return matchSetters(request);
+    }
+
+    String msg = "Unable to map the resultSet columns " + Arrays.toString(cols)
+      + " to the bean type ["+dtoType+"] as the number of columns in the resultSet is less than the constructor"
+      + " (and that there is no default constructor) ?";
+    throw new IllegalStateException(msg);
+  }
+
+  private DtoQueryPlanConPlus matchMaxArgPlusSetters(DtoMappingRequest request) {
+
+
+    int firstOnes = maxArgConstructor.getArgCount();
+
+    DtoColumn[] cols = request.getColumnMeta();
+
+    DtoReadSet[] setterProps = new DtoReadSet[cols.length - firstOnes];
+
+    int pos = 0;
+    for (int i = firstOnes; i < cols.length; i++) {
+      String label = cols[i].getLabel();
+      DtoReadSet property = propMap.get(label.toUpperCase());
+      if (property == null || property.isReadOnly()) {
+        if (request.isRelaxedMode()) {
+          property = DtoReadSetColumnSkip.INSTANCE;
+        } else {
+          throw new IllegalStateException("Unable to map DB column " + cols[i] + " to a property with a setter method on " + dtoType);
+        }
+      }
+      setterProps[pos++] = property;
+    }
+
+    return new DtoQueryPlanConPlus(request, maxArgConstructor, setterProps);
+  }
+
+  private DtoQueryPlan matchSetters(DtoMappingRequest request) {
+
+    DtoColumn[] cols = request.getColumnMeta();
+
+    DtoReadSet[] setterProps = new DtoReadSet[cols.length];
+
+    for (int i = 0; i < cols.length; i++) {
+      String label = cols[i].getLabel();
+      DtoReadSet property = propMap.get(label.toUpperCase());
+      if (property == null || property.isReadOnly()) {
+        if (request.isRelaxedMode()) {
+          property = DtoReadSetColumnSkip.INSTANCE;
+        } else {
+          throw new IllegalStateException("Unable to map DB column " + cols[i] + " to a property with a setter method on " + dtoType);
+        }
+      }
+      setterProps[i] = property;
+    }
+
+    return new DtoQueryPlanConSetter(request, defaultConstructor, setterProps);
+  }
+}