Say: there is already a given schema definition object:
const schema = { prop1: { type: String, maxLength: 8 }, prop2... };
Is it possible that: without declare the interface for each schema object, make a respective class which can produce documents with prop1:string, prop2... extracted from the schema.
I expect something like this in my app:
// schema definition:
const PersonSchema = { name: { type: String, maxLength: 8 } };
// class factory
const PersonClass = SchemaClassFactory(PersonSchema);
// instance with props defined in schema.
let person1 = new PersonClass();
person1.name = 'Jack';
let person2 = new PersonClass();
person2.name = 3; // should be wrong hinted by tslint.
How can I achieve that?
You can create a class for the schema object using a mapped type and conditional types to extract the shape of the object from the schema.
A possible solution is below, I am not sure I covered all the ways you can defined the schema in mongoose, but this should get you stared:
const PersonSchema = {
name: { type: String, maxLength: 8 },
age: { type: Number },
title: String,
id: ObjectID
};
type PrimitiveConstructor<T> = {
new (...a: any[]): any;
(...a: any[]): T
}
type Constructor<T> = {
new (...a: any[]): T;
}
type ExtractType<T> = {
[P in keyof T] :
T[P] extends PrimitiveConstructor<infer U>? U :
T[P] extends { type: PrimitiveConstructor<infer U> } ? U:
T[P] extends Constructor<infer U> ? U :
T[P] extends { type: Constructor<infer U> } ? U:
never
}
function createClass<T>(schema: T): new (data?: Partial<ExtractType<T>>) => ExtractType<T> {
// The class will not have the fields explicitly defined since we don't know them but that is fine
return new class {
// Optional constructor for assigning data to the fields, you can remove this if not needed
constructor(data?: any){
if(data) {
Object.assign(this, data);
}
}
} as any;
}
var PersonClass = createClass(PersonSchema);
type PersonClass = InstanceType<typeof PersonClass>
let p = new PersonClass();
p.name ="";
p.name = 2; // error
p.id = new ObjectID(10);
let p2 = new PersonClass({
name: "",
});
Please how do we construct a dynamic where filter in EF.Core to handle:
Query.Where(fieldName, compareMode, value)
I basically Expect to use it like below:
[HttpGet(Name = nameof(GetStaff))]
public IActionResult GetStaffAsync([FromQuery] QueryParams p)
{
var s = db.Staff.AsNoTracking()
.Where(p.filter_field, p.filter_mode, p.filter_value)
.OrderByMember(p.sortBy, p.descending);
var l = new Pager<Staff>(s, p.page, p.rowsPerPage);
return Ok(l);
}
//Helpers
public class QueryParams
{
public bool descending { get; set; }
public int page { get; set; } = 1;
public int rowsPerPage { get; set; } = 5;
public string sortBy { get; set; }
public onject filter_value { get; set; }
public string filter_field { get; set; }
public string filter_mode { get; set; }
}
public class Pager<T>
{
public int pages { get; set; }
public int total { get; set; }
public IEnumerable<T> Items { get; set; }
public Pager(IEnumerable<T> items, int offset, int limit)
{
Items = items.Skip((offset - 1) * limit).Take(limit).ToList<T>();
total = items.Count();
pages = (int)Math.Ceiling((double)total / limit);
}
}
Assuming all you have is the entity type and strings representing the property, comparison operator and the value, building dynamic predicate can be done with something like this:
public static partial class ExpressionUtils
{
public static Expression<Func<T, bool>> BuildPredicate<T>(string propertyName, string comparison, string value)
{
var parameter = Expression.Parameter(typeof(T), "x");
var left = propertyName.Split('.').Aggregate((Expression)parameter, Expression.Property);
var body = MakeComparison(left, comparison, value);
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
private static Expression MakeComparison(Expression left, string comparison, string value)
{
switch (comparison)
{
case "==":
return MakeBinary(ExpressionType.Equal, left, value);
case "!=":
return MakeBinary(ExpressionType.NotEqual, left, value);
case ">":
return MakeBinary(ExpressionType.GreaterThan, left, value);
case ">=":
return MakeBinary(ExpressionType.GreaterThanOrEqual, left, value);
case "<":
return MakeBinary(ExpressionType.LessThan, left, value);
case "<=":
return MakeBinary(ExpressionType.LessThanOrEqual, left, value);
case "Contains":
case "StartsWith":
case "EndsWith":
return Expression.Call(MakeString(left), comparison, Type.EmptyTypes, Expression.Constant(value, typeof(string)));
default:
throw new NotSupportedException($"Invalid comparison operator '{comparison}'.");
}
}
private static Expression MakeString(Expression source)
{
return source.Type == typeof(string) ? source : Expression.Call(source, "ToString", Type.EmptyTypes);
}
private static Expression MakeBinary(ExpressionType type, Expression left, string value)
{
object typedValue = value;
if (left.Type != typeof(string))
{
if (string.IsNullOrEmpty(value))
{
typedValue = null;
if (Nullable.GetUnderlyingType(left.Type) == null)
left = Expression.Convert(left, typeof(Nullable<>).MakeGenericType(left.Type));
}
else
{
var valueType = Nullable.GetUnderlyingType(left.Type) ?? left.Type;
typedValue = valueType.IsEnum ? Enum.Parse(valueType, value) :
valueType == typeof(Guid) ? Guid.Parse(value) :
Convert.ChangeType(value, valueType);
}
}
var right = Expression.Constant(typedValue, left.Type);
return Expression.MakeBinary(type, left, right);
}
}
Basically building property accessor (with nested property support), parsing the comparison operator and calling the corresponding operator/method, dealing with from/to string and from/to nullable type conversions. It can be extended to handle EF Core specific functions like EF.Functions.Like by adding the corresponding branch.
It can be used directly (in case you need to combine it with other predicates) or via custom extension method like this:
public static partial class QueryableExtensions
{
public static IQueryable<T> Where<T>(this IQueryable<T> source, string propertyName, string comparison, string value)
{
return source.Where(ExpressionUtils.BuildPredicate<T>(propertyName, comparison, value));
}
}
based on Ivans answer this is what i came up with
public static class ExpressionUtils
{
public static Expression<Func<T, bool>> BuildPredicate<T>(string propertyName, string comparison, object value)
{
var parameter = Expression.Parameter(typeof(T));
var left = propertyName.Split('.').Aggregate((Expression)parameter, Expression.PropertyOrField);
var body = MakeComparison(left, comparison, value);
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
static Expression MakeComparison(Expression left, string comparison, object value)
{
var constant = Expression.Constant(value, left.Type);
switch (comparison)
{
case "==":
return Expression.MakeBinary(ExpressionType.Equal, left, constant);
case "!=":
return Expression.MakeBinary(ExpressionType.NotEqual, left, constant);
case ">":
return Expression.MakeBinary(ExpressionType.GreaterThan, left, constant);
case ">=":
return Expression.MakeBinary(ExpressionType.GreaterThanOrEqual, left, constant);
case "<":
return Expression.MakeBinary(ExpressionType.LessThan, left, constant);
case "<=":
return Expression.MakeBinary(ExpressionType.LessThanOrEqual, left, constant);
case "Contains":
case "StartsWith":
case "EndsWith":
if (value is string)
{
return Expression.Call(left, comparison, Type.EmptyTypes, constant);
}
throw new NotSupportedException($"Comparison operator '{comparison}' only supported on string.");
default:
throw new NotSupportedException($"Invalid comparison operator '{comparison}'.");
}
}
}
and some tests
public class Tests
{
[Fact]
public void Nested()
{
var list = new List<Target>
{
new Target
{
Member = "a"
},
new Target
{
Member = "bb"
}
};
var result = list.AsQueryable()
.Where(ExpressionUtils.BuildPredicate<Target>("Member.Length", "==", 2))
.Single();
Assert.Equal("bb", result.Member);
}
[Fact]
public void Field()
{
var list = new List<TargetWithField>
{
new TargetWithField
{
Field = "Target1"
},
new TargetWithField
{
Field = "Target2"
}
};
var result = list.AsQueryable()
.Where(ExpressionUtils.BuildPredicate<TargetWithField>("Field", "==", "Target2"))
.Single();
Assert.Equal("Target2", result.Field);
}
[Theory]
[InlineData("Name", "==", "Person 1", "Person 1")]
[InlineData("Name", "!=", "Person 2", "Person 1")]
[InlineData("Name", "Contains", "son 2", "Person 2")]
[InlineData("Name", "StartsWith", "Person 2", "Person 2")]
[InlineData("Name", "EndsWith", "son 2", "Person 2")]
[InlineData("Age", "==", 13, "Person 2")]
[InlineData("Age", ">", 12, "Person 2")]
[InlineData("Age", "!=", 12, "Person 2")]
[InlineData("Age", ">=", 13, "Person 2")]
[InlineData("Age", "<", 13, "Person 1")]
[InlineData("Age", "<=", 12, "Person 1")]
public void Combos(string name, string expression, object value, string expectedName)
{
var people = new List<Person>
{
new Person
{
Name = "Person 1",
Age = 12
},
new Person
{
Name = "Person 2",
Age = 13
}
};
var result = people.AsQueryable()
.Where(ExpressionUtils.BuildPredicate<Person>(name, expression, value))
.Single();
Assert.Equal(expectedName, result.Name);
}
}
I modified the answer I found here: Linq WHERE EF.Functions.Like - Why direct properties work and reflection does not?
I chucked together a version for those using NpgSQL as their EF Core provider as you will need to use the ILike function instead if you want case-insensitivity, also added a second version which combines a bunch of properties into a single Where() clause:
public static IQueryable<T> WhereLike<T>(this IQueryable<T> source, string propertyName, string searchTerm)
{
// Check property name
if (string.IsNullOrEmpty(propertyName))
{
throw new ArgumentNullException(nameof(propertyName));
}
// Check the search term
if(string.IsNullOrEmpty(searchTerm))
{
throw new ArgumentNullException(nameof(searchTerm));
}
// Check the property exists
var property = typeof(T).GetProperty(propertyName);
if (property == null)
{
throw new ArgumentException($"The property {typeof(T)}.{propertyName} was not found.", nameof(propertyName));
}
// Check the property type
if(property.PropertyType != typeof(string))
{
throw new ArgumentException($"The specified property must be of type {typeof(string)}.", nameof(propertyName));
}
// Get expression constants
var searchPattern = "%" + searchTerm + "%";
var itemParameter = Expression.Parameter(typeof(T), "item");
var functions = Expression.Property(null, typeof(EF).GetProperty(nameof(EF.Functions)));
var likeFunction = typeof(NpgsqlDbFunctionsExtensions).GetMethod(nameof(NpgsqlDbFunctionsExtensions.ILike), new Type[] { functions.Type, typeof(string), typeof(string) });
// Build the property expression and return it
Expression selectorExpression = Expression.Property(itemParameter, property.Name);
selectorExpression = Expression.Call(null, likeFunction, functions, selectorExpression, Expression.Constant(searchPattern));
return source.Where(Expression.Lambda<Func<T, bool>>(selectorExpression, itemParameter));
}
public static IQueryable<T> WhereLike<T>(this IQueryable<T> source, IEnumerable<string> propertyNames, string searchTerm)
{
// Check property name
if (!(propertyNames?.Any() ?? false))
{
throw new ArgumentNullException(nameof(propertyNames));
}
// Check the search term
if (string.IsNullOrEmpty(searchTerm))
{
throw new ArgumentNullException(nameof(searchTerm));
}
// Check the property exists
var properties = propertyNames.Select(p => typeof(T).GetProperty(p)).AsEnumerable();
if (properties.Any(p => p == null))
{
throw new ArgumentException($"One or more specified properties was not found on type {typeof(T)}: {string.Join(",", properties.Where(p => p == null).Select((p, i) => propertyNames.ElementAt(i)))}.", nameof(propertyNames));
}
// Check the property type
if (properties.Any(p => p.PropertyType != typeof(string)))
{
throw new ArgumentException($"The specified properties must be of type {typeof(string)}: {string.Join(",", properties.Where(p => p.PropertyType != typeof(string)).Select(p => p.Name))}.", nameof(propertyNames));
}
// Get the expression constants
var searchPattern = "%" + searchTerm + "%";
var itemParameter = Expression.Parameter(typeof(T), "item");
var functions = Expression.Property(null, typeof(EF).GetProperty(nameof(EF.Functions)));
var likeFunction = typeof(NpgsqlDbFunctionsExtensions).GetMethod(nameof(NpgsqlDbFunctionsExtensions.ILike), new Type[] { functions.Type, typeof(string), typeof(string) });
// Build the expression and return it
Expression selectorExpression = null;
foreach (var property in properties)
{
var previousSelectorExpression = selectorExpression;
selectorExpression = Expression.Property(itemParameter, property.Name);
selectorExpression = Expression.Call(null, likeFunction, functions, selectorExpression, Expression.Constant(searchPattern));
if(previousSelectorExpression != null)
{
selectorExpression = Expression.Or(previousSelectorExpression, selectorExpression);
}
}
return source.Where(Expression.Lambda<Func<T, bool>>(selectorExpression, itemParameter));
}
I have multple models in bookself:
User (id, username)
Team (id, name)
Skill (id, name)
TeamSkill (id, skill_id, team_id)
TeamSkillUpvote (id, team_skill_id, user_id)
I would like to make this kind of query:
select team.id, team.name, team_skill_upvotes.user_id
from skill, team_skills, team
where skill.id = <THE_ID_OF_MY_MODEL>
and skill.id = team_skills.skill_id
and team_skills.team_id = team.id
and team_skills.id = team_skill_upvotes.team_skill_id
Anyone can help?
Thanks!
After searching I found the answer...It is built in a few steps:
1: Define relations for the TeamSkill:
export interface ITeamSkillRelations {
team: Team;
upvotes: Collection<TeamSkillUpvote>;
}
export class TeamSkill extends bookshelf.Model<TeamSkill>{
...
public relations: ITeamSkillRelations;
public upvotes(): Collection<TeamSkillUpvote> {
return this.hasMany(TeamSkillUpvote, TeamSkillUpvote.teamSkillIdAttribute/*team_skill_id*/);
}
public team(): Team {
return this.belongsTo(Team, TeamSkill.teamIdAttribute/*team_id*/);
}
...
}
2: The magic:
export class Skill extends bookshelf.Model<Skill> {
public getTeams(): Promise<ITeamOfASkill[]> {
var fetchOptions: CollectionFetchOptions = {
withRelated: [
TeamSkill.relatedTeamSkillUpvotesAttribute/*upvotes*/,
TeamSkill.relatedTeamAttribute/*team*/
]
};
return this.teamSkills()
.fetch(fetchOptions)
.then((teamSkillsCollection: Collection<TeamSkill>) => {
var teamSkills: TeamSkill[] = teamSkillsCollection.toArray();
return _.map(teamSkills, _skill => this._convertTeamSkillToTeamOfASkill(_skill));
});
}
private _convertTeamSkillToTeamOfASkill(teamSkill: TeamSkill): ITeamOfASkill {
var team: Team = teamSkill.relations.team;
var upvotesCollection: Collection<TeamSkillUpvote> = teamSkill.relations.upvotes;
var upvotes: TeamSkillUpvote[] = upvotesCollection.toArray();
var upvotingIds =
_.map(upvotes, _ => _.attributes.user_id);
return {
team: team,
upvotingUserIds: upvotingIds
};
}
}