// This takes a Queryable<T> as an object, and executes a T-typed method call against it
// That is, you define a `call` in terms of Queryable<object> and it will be converted to Queryable<T>
//
// ex: GenericQueryableCall(queryableAsObj, q => q.FirstOrDefault());
//
// In this case, the generic method is represented at compiled time as FirstOrDefault<object>.
// However, the generic type is replaced at runtime to FirstOrDefault<T> then dynamically invoked on `queryable`
//
// This is necessary for NHibernate, which inspects the generic type of the method executing the queryable.
// So, if the queryable is of compile-time type IQueryable<object> instead of IQueryable<TEntity>, NHibernate will fail on execution
private static TReturn GenericQueryableCall <TReturn>(object queryable, Expression <Func <IQueryable <object>, TReturn> > call)
{
var entityType = queryable.GetType().GetGenericArguments()[0];
var mce = call.Body as MethodCallExpression;
var genericMethod = mce.Method.GetGenericMethodDefinition();
var newMethod = genericMethod.MakeGenericMethod(entityType);
var newParameter = Expression.Parameter(typeof(IQueryable <>).MakeGenericType(entityType));
var newArguments = mce.Arguments.Select(a => ParameterReplacer.Replace(a, call.Parameters[0], newParameter));
var newCall = Expression.Call(newMethod, newArguments);
var newLambda = Expression.Lambda(newCall, newParameter);
return((TReturn)newLambda.Compile().DynamicInvoke(queryable));
}
private static MemberBinding GetBinding(FieldMap map, Type toType, Expression baseBindingExpr, int n)
{
var mapFieldName = $"Field{n}";
var toMember = toType.GetMember(mapFieldName)[0];
var expr = map.SchemaField.GetExpression(new List <Input>()); // TODO: real inputs
var replacedBase = ParameterReplacer.Replace(expr.Body, expr.Parameters[1], baseBindingExpr);
var replacedContext = ParameterReplacer.Replace(replacedBase, expr.Parameters[0], GraphQLSchema <TContext> .DbParam);
if (!map.Children.Any())
{
return(Expression.Bind(toMember, replacedContext));
}
var memberInit = GetMemberInit(map.Children, replacedContext);
return(Expression.Bind(toType.GetMember(mapFieldName)[0], memberInit));
}
public static IDictionary <string, object> Execute <TArgs, TEntity>(TContext context, GraphQLQuery <TContext, TArgs, TEntity> gqlQuery, Query query)
{
var args = TypeHelpers.GetArgs <TArgs>(query.Inputs);
var queryableFuncExpr = gqlQuery.QueryableExprGetter(args);
var replaced = (Expression <Func <TContext, IQueryable <TEntity> > >)ParameterReplacer.Replace(queryableFuncExpr, queryableFuncExpr.Parameters[0], GraphQLSchema <TContext> .DbParam);
var fieldMaps = query.Fields.Select(f => MapField(f, gqlQuery.Type)).ToList();
var selector = GetSelector <TEntity>(fieldMaps);
var selectorExpr = Expression.Quote(selector);
var call = Expression.Call(typeof(Queryable), "Select", new[] { typeof(TEntity), typeof(GQLQueryObject20) }, replaced.Body, selectorExpr);
var expr = (Expression <Func <TContext, IQueryable <GQLQueryObject20> > >)Expression.Lambda(call, GraphQLSchema <TContext> .DbParam);
var transformed = expr.Compile()(context);
object results;
switch (gqlQuery.ResolutionType)
{
case ResolutionType.Unmodified:
throw new Exception("Queries cannot have unmodified resolution. May change in the future.");
case ResolutionType.ToList:
results = transformed.ToList().Select(o => MapResults(o, fieldMaps));
break;
case ResolutionType.FirstOrDefault:
results = MapResults(transformed.FirstOrDefault(), fieldMaps);
break;
case ResolutionType.First:
results = MapResults(transformed.First(), fieldMaps);
break;
default:
throw new ArgumentOutOfRangeException();
}
return(new Dictionary <string, object> {
{ "data", results }
});
}
private static MemberBinding GetBinding(GraphQLSchema <TContext> schema, ExecSelection <Info> map, Type toType, Expression baseBindingExpr, ExpressionOptions options)
{
var field = map.SchemaField.Field();
var needsTypeCheck = baseBindingExpr.Type != field.DefiningType.CLRType;
var toMember = toType.GetProperty(map.SchemaField.FieldName);
// expr is form of: (context, entity) => entity.Field
var expr = field.GetExpression(map.Arguments.Values());
// The field might be defined on sub-types of the specified type, so add a type cast if necessary.
// If appropriate, `entity.Field` becomes `(entity as TFieldDefiningType).Field`
var typeCastedBaseExpression = needsTypeCheck ? Expression.TypeAs(baseBindingExpr, field.DefiningType.CLRType) : baseBindingExpr;
// Replace (entity) with baseBindingExpr, note expression is no longer a LambdaExpression
// `(context, entity) => entity.Field` becomes `someOtherEntity.Entity.Field` where baseBindingExpr is `someOtherEntity.Entity`
var replacedBase = ParameterReplacer.Replace(expr.Body, expr.Parameters[1], typeCastedBaseExpression);
// If the entity has to be casted, add a type check:
// `(someOtherEntity.Entity as TFieldDefininingType).Field` becomes `(someOtherEntity.Entity is TFieldDefininingType) ? (someOtherEntity.Entity as TFieldDefininingType).Field : null`
if (needsTypeCheck && options.TypeCheckInheritance)
{
// The expression type has to be nullable
if (replacedBase.Type.IsValueType)
{
replacedBase = Expression.Convert(replacedBase, typeof(Nullable <>).MakeGenericType(replacedBase.Type));
}
var typeCheck = Expression.TypeIs(baseBindingExpr, field.DefiningType.CLRType);
var nullResult = Expression.Constant(null, replacedBase.Type);
replacedBase = Expression.Condition(typeCheck, replacedBase, nullResult);
}
// This just makes sure that the (context) parameter is the same as the one used by the whole query
var replacedContext = ParameterReplacer.Replace(replacedBase, expr.Parameters[0], GraphQLSchema <TContext> .DbParam);
// If there aren't any children, then we can assume that this is a scalar entity and we don't have to map child fields
if (!map.Selections.Any())
{
if (options.CastAssignment && expr.Body.Type != toMember.PropertyType)
{
replacedContext = Expression.Convert(replacedContext, toMember.PropertyType);
}
return(Expression.Bind(toMember, replacedContext));
}
// If binding a single entity, just use the already built selector expression (replaced context)
// Otherwise, if binding to a list, introduce a new parameter that will be used in a call to .Select
var listParameter = Expression.Parameter
(field.Type.CLRType, field.Type.CLRType.Name.Substring(0, 1).ToLower()); // TODO: Name conflicts in expressions?
var bindChildrenTo = map.SchemaField.Field().IsList ? listParameter : replacedContext;
// Now that we have our new binding parameter, build the tree for the rest of the children
var memberInit = GetMemberInit(schema, field.Type.QueryType, map.Selections.Values(), bindChildrenTo, options);
// For single entities, we're done and we can just bind to the memberInit expression
if (!field.IsList)
{
return(Expression.Bind(toMember, memberInit));
}
// However for lists, we need to check for null and call .Select() and .ToList() first
var selectLambda = Expression.Lambda(memberInit, listParameter);
var call = Expression.Call(typeof(Enumerable), "Select", new[] { field.Type.CLRType, field.Type.QueryType }, replacedContext, selectLambda);
var toList = Expression.Call(typeof(Enumerable), "ToList", new[] { field.Type.QueryType }, call);
return(Expression.Bind(toMember, options.NullCheckLists ? (Expression)NullPropagate(replacedContext, toList) : toList));
}
public static object Execute
(GraphQLSchema <TContext> schema, TContext context, GraphQLField field, ExecSelection <Info> query)
{
var mutReturn = field.RunMutation(context, query.Arguments.Values());
var queryableFuncExpr = field.GetExpression(query.Arguments.Values(), mutReturn);
var replaced = (LambdaExpression)ParameterReplacer.Replace(queryableFuncExpr, queryableFuncExpr.Parameters[0], GraphQLSchema <TContext> .DbParam);
// sniff queryable provider to determine how selector should be built
var dummyQuery = replaced.Compile().DynamicInvoke(context, null);
var queryType = dummyQuery.GetType();
var expressionOptions = schema.GetOptionsForQueryable(queryType);
if (expressionOptions.UseBaseType)
{
queryType = queryType.BaseType;
expressionOptions = schema.GetOptionsForQueryable(queryType);
}
var queryExecSelections = query.Selections.Values();
var selector = GetSelector(schema, field.Type, queryExecSelections, expressionOptions);
if (field.ResolutionType != ResolutionType.Unmodified)
{
var selectorExpr = Expression.Quote(selector);
// TODO: This should be temporary - queryable and enumerable should both work
var body = replaced.Body;
if (body.NodeType == ExpressionType.Convert)
{
body = ((UnaryExpression)body).Operand;
}
var call = Expression.Call(typeof(Queryable), "Select", new[] { field.Type.CLRType, field.Type.QueryType }, body, selectorExpr);
var expr = Expression.Lambda(call, GraphQLSchema <TContext> .DbParam);
var transformed = expr.Compile().DynamicInvoke(context);
object results;
switch (field.ResolutionType)
{
case ResolutionType.Unmodified:
throw new Exception("Queries cannot have unmodified resolution. May change in the future.");
case ResolutionType.ToList:
var list = GenericQueryableCall <IEnumerable <object> >(transformed, q => q.ToList());
results = list.Select(o => MapResults(o, queryExecSelections, schema)).ToList();
break;
case ResolutionType.FirstOrDefault:
var fod = GenericQueryableCall(transformed, q => q.FirstOrDefault());
results = MapResults(fod, queryExecSelections, schema);
break;
case ResolutionType.First:
var first = GenericQueryableCall(transformed, q => q.FirstOrDefault());
results = MapResults(first, queryExecSelections, schema);
break;
default:
throw new ArgumentOutOfRangeException();
}
return(results);
}
else
{
var invocation = Expression.Invoke(selector, replaced.Body);
var expr = Expression.Lambda(invocation, GraphQLSchema <TContext> .DbParam);
var result = expr.Compile().DynamicInvoke(context);
return(MapResults(result, queryExecSelections, schema));
}
}